Border Security: Immigration Enforcement
Between Ports of Entry
Lisa Seghetti
Section Research Manager
December 18, 2014
Congressional Research Service
7-5700
www.crs.gov
R42138
Border Security: Immigration Enforcement Between Ports of Entry
Summary
Border enforcement is a core element of the Department of Homeland Security’s effort to control
unauthorized migration, with the U.S. Border Patrol (USBP) within the U.S. Customs and Border
Protection (CBP) as the lead agency along most of the border. Border enforcement has been an
ongoing subject of congressional interest since the 1970s, when illegal immigration to the United
States first registered as a serious national problem; and border security has received additional
attention in the years since the terrorist attacks of 2001.
Since the 1990s, migration control at the border has been guided by a strategy of “prevention
through deterrence”—the idea that the concentration of personnel, infrastructure, and surveillance
technology along heavily trafficked regions of the border will discourage unauthorized aliens
from attempting to enter the United States. Since 2005, CBP has attempted to discourage repeat
illegal migrant entries and disrupt migrant smuggling networks by imposing tougher penalties
against certain unauthorized aliens, a set of policies eventually described as “enforcement with
consequences.” Most people apprehended at the Southwest border are now subject to “high
consequence” enforcement outcomes.
Across a variety of indicators, the United States has substantially expanded border enforcement
resources over the last three decades. Particularly since 2001, such increases include border
security appropriations, personnel, fencing and infrastructure, and surveillance technology. In
addition to increased resources, the USBP has implemented several strategies over the past
several decades in an attempt to thwart illegal migration. Recently, the Obama Administration
announced executive actions to “fix” the immigration system. These actions address numerous
issues, including a security plan at the southern border.
The Border Patrol collects data on several different border enforcement outcomes; and this report
describes trends in border apprehensions, recidivism, and estimated got aways and turn backs. Yet
none of these existing data are designed to measure illegal border flows or the degree to which
the border is secured. Thus, the report also describes methods for estimating illegal border flows
based on enforcement data and migrant surveys.
Drawing on multiple data sources, the report suggests conclusions about the state of border
security. Robust investments at the border were not associated with reduced illegal inflows during
the 1980s and 1990s, but a range of evidence suggests a substantial drop in illegal inflows in
2007-2011, followed by a slight rise in 2012 and a more dramatic rise in 2013. Enforcement,
along with the economic downturn in the United States, likely contributed to the drop in
unauthorized migration, though the precise share of the decline attributable to enforcement is
unknown.
Enhanced border enforcement also may have contributed to a number of secondary costs and
benefits. To the extent that border enforcement successfully deters illegal entries, such
enforcement may reduce border-area violence and migrant deaths, protect fragile border
ecosystems, and improve the quality of life in border communities. But to the extent that aliens
are not deterred, the concentration of enforcement resources on the border may increase border
area violence and migrant deaths, encourage unauthorized migrants to find new ways to enter
illegally and to remain in the United States for longer periods of time, damage border ecosystems,
harm border-area businesses and the quality of life in border communities, and strain U.S.
relations with Mexico and Canada.
Congressional Research Service
Border Security: Immigration Enforcement Between Ports of Entry
Contents
Introduction ...................................................................................................................................... 1
Border Patrol History and Strategy .................................................................................................. 2
Border Patrol Strategic Plans ..................................................................................................... 3
National Strategic Plan ........................................................................................................ 3
National Border Patrol Strategy .......................................................................................... 4
Border Patrol Strategic Plan ................................................................................................ 5
DHS Secure Border Initiative .................................................................................................... 6
CBP Consequence Delivery System .......................................................................................... 7
Southern Border Campaign Plan ............................................................................................. 12
Budget and Resources .................................................................................................................... 12
Border Security Appropriations ............................................................................................... 12
Border Patrol Personnel ........................................................................................................... 14
National Guard Troops at the Border ................................................................................ 15
Fencing and Tactical Infrastructure ......................................................................................... 16
Surveillance Assets .................................................................................................................. 18
Aerial and Marine Surveillance ......................................................................................... 19
Border Patrol Enforcement Data .................................................................................................... 20
Alien Apprehensions ............................................................................................................... 20
Southwest Border Apprehensions by Sector ..................................................................... 21
Unique Subjects and Alien Recidivism ................................................................................... 22
Estimated “Got Aways” and “Turn Backs” ............................................................................. 24
Additional Border Security Data: Migrant Surveys ....................................................................... 24
Probability of Apprehension .................................................................................................... 25
Border Deterrence ................................................................................................................... 25
Smuggling Fees ....................................................................................................................... 26
Metrics of Border Security ............................................................................................................ 27
The Residual Method for Estimating Unauthorized Residents in the United States ............... 29
CBP Metrics of Border Security .............................................................................................. 30
Operational Control of the Border .................................................................................... 30
Border Conditions Index ................................................................................................... 30
Border Patrol Effectiveness Rate ...................................................................................... 31
Estimating Illegal Flows Using Recidivism Data .................................................................... 31
How Secure is the U.S. Border? .................................................................................................... 32
Unintended and Secondary Consequences of Border Enforcement .............................................. 35
Border-Area Crime and Migrant Deaths ................................................................................. 35
Migration Flows: “Caging” Effects and Alternative Modes of Entry ..................................... 38
Environmental Impact ............................................................................................................. 39
Effects on Border Communities and Civil Rights ................................................................... 39
Effects on Regional Relations ................................................................................................. 41
Conclusion: Understanding the Costs and Benefits of Border Enforcement between Ports
of Entry ....................................................................................................................................... 41
Congressional Research Service
Border Security: Immigration Enforcement Between Ports of Entry
Figures
Figure 1. CBP “Enforcement with Consequences,” FY2005-FY2012 .......................................... 10
Figure 2. U.S. Border Patrol Appropriations, FY1989-FY2014 .................................................... 13
Figure 3. U.S. Border Patrol Agents, Total and by Region, FY1980-FY2013 .............................. 15
Figure 4. Tactical Infrastructure Appropriations and Miles of Border Fencing, FY1996-
FY2013 ....................................................................................................................................... 17
Figure 5. Total USBP Apprehensions of Deportable Aliens, FY1960-FY2012 ............................. 21
Figure 6. U.S. Border Patrol Apprehensions of Deportable Aliens, Southwest Border, by
Selected Sectors, FY1992-FY2013 ............................................................................................ 22
Figure 7. USBP Southwest Border Unique Subjects and Recidivism Rates ................................. 23
Figure 8. Smuggling Fees Paid by Unauthorized Mexican Migrants, 1980-2010 ......................... 27
Figure 9. Total Estimated Illegal Border Inflows, by Assumed Rate of Deterrence ...................... 34
Figure 10. Known Migrant Deaths, Southwest Border, 1985-2012 .............................................. 37
Tables
Table 1. Consequence Delivery System Outcomes and Recidivism Rates .................................... 11
Appendixes
Appendix. Capture-Recapture Methodology ................................................................................. 43
Contacts
Author Contact Information........................................................................................................... 44
Acknowledgments ......................................................................................................................... 44
Congressional Research Service
Border Security: Immigration Enforcement Between Ports of Entry
Introduction
The country’s immigration and naturalization laws have been subjects of episodic controversy
since America’s founding, but illegal immigration only became an issue in the early 20th century,
when Congress passed the first strict restrictions on legal admissions. Illegal immigration
declined during the Great Depression and during and after World War II, when most labor
migration occurred through the U.S.-Mexico Bracero program.1 Immigration control re-emerged
as a national concern during the 1970s, when the end of the Bracero program, new restrictions on
Western Hemisphere migration, and growing U.S. demand for foreign-born workers combined to
cause a sharp increase in unauthorized migration flows.2
Congress responded in 1986 by passing the Immigration Reform and Control Act (IRCA, P.L. 99-
603), which authorized a 50% increase in Border Patrol staffing, among other provisions. Border
security3 has remained a persistent topic of congressional interest since then, and enforcement
programs and appropriations have grown accordingly, as described in this report.
Despite a growing enforcement response, however, illegal immigration continued to increase over
most of the next three decades.4 Unauthorized migration declined after 2007; however, in 2013
the number of unauthorized migrants increased to 13.1 million.5 Apprehensions of unauthorized
migrants at the U.S.-Mexico border fell from about 1.2 million in FY2005 to a 41-year low of
328,000 in 2011, before climbing to 357,000 in FY2012. Apprehensions of unauthorized migrants
at the U.S.-Mexico border increased to 479,377 in FY2014.6
Recently, the Obama Administration announced executive actions to “fix” the immigration
system.7 These actions address numerous issues, including a security plan at the southern border.
Some Members of Congress and state officials, however, disagree with the President’s plan and
have called on the Administration to do more to secure the border.8 Border security has been a
1 The Bracero program was a formal guest worker program managed jointly by the United States and Mexico that
admitted about 4.6 million workers between 1942 and 1964.
2 The estimated population of unauthorized aliens was about 1.7 million by 1979 and about 3.2 million in 1986; most
researchers, however, consider earlier estimates of the unauthorized population to be unreliable. See Jennifer Van Hook
and Frank D. Bean, “Estimating Unauthorized Mexican Migration to the United States: Issues and Trends,” in
Binational Study: Migration Between Mexico and the United States (Washington, DC: US Commission on Immigration
Reform, 1998), pp. 538-540.
3 Except as otherwise noted, this report focuses exclusively on border security as it relates to the prevention of
unauthorized migration. On the relationship among unauthorized migration, illegal drugs and other contraband,
international terrorists, and other types of border threats, see CRS Report R42969, Border Security: Understanding
Threats at U.S. Borders, by Jerome P. Bjelopera and Kristin Finklea.
4 See archived CRS Report RL33874, Unauthorized Aliens Residing in the United States: Estimates Since 1986, by
Ruth Ellen Wasem.
5 See CRS Report R42988, U.S. Immigration Policy: Chart Book of Key Trends, by William A. Kandel.
6 Department of Homeland Security press release, remarks by Secretary of Homeland Security Jeh Johnson (and
accompanying slides), “Border Security in the 21st Century,” October 9, 2014 (Hereafter referred to as “Border
Security in the 21st Century”). The spike in apprehensions in FY2014 can be largely attributed to the unaccompanied
alien children crisis. See CRS Report R43599, Unaccompanied Alien Children: An Overview.
7 See DHS “Fixing Our Immigration Broken System Through Executive Action – Key Facts” at http://www.dhs.gov/
immigration-action?utm_source=hp_feature&utm_medium=web&utm_campaign=dhs_hp.
8 Led by Texas, 17 states have moved to sue President Obama over his executive action on immigration. “17 States
Suing on Immigration.” The New York Times, December 3, 2014, http://www.nytimes.com/2014/12/04/us/executive-
action-on-immigration-prompts-texas-to-sue.html?_r=0.
Congressional Research Service
1
Border Security: Immigration Enforcement Between Ports of Entry
recurrent theme in Congress’s debate about immigration reform since 2005, and some Members
of Congress have argued that Congress should not consider additional immigration reforms until
the border is more secure.9
This report reviews efforts to combat unauthorized migration across the Southwest border in the
nearly three decades since IRCA initiated the modern era in migration control. In reviewing such
efforts, the report takes stock of the current state of border security and considers lessons that
may be learned about enhanced enforcement at U.S. borders. The report begins by reviewing the
history of border control and the development of a national border control strategy beginning in
the 1990s. The following sections summarize appropriations and resources dedicated to border
enforcement, indicators of enforcement outcomes, metrics for estimating unauthorized migration
flows, and possible secondary and unintended consequences of border enforcement. The report
concludes by reviewing the overall costs and benefits of the current approach to migration control
and raising additional questions that may help guide the discussion of these issues in the future.
Border Patrol History and Strategy
Congress created the U.S. Border Patrol (USBP) within the Department of Commerce and Labor
by an appropriations act in 1924,10 two days after passing the first permanent numeric
immigration restrictions.11 Numerical limits only applied to the Eastern Hemisphere, barring most
Asian immigration; and the Border Patrol’s initial focus was on preventing the entry of Chinese
migrants, as well as combating gun trafficking and alcohol imports during prohibition. The
majority of agents were stationed on the northern border.12 The Border Patrol became part of the
new Immigration and Naturalization Service (INS) in 1933, and the INS moved from the
Department of Labor to the Department of Justice in 1940. The Border Patrol’s focus shifted to
the Southwest border during World War II, but preventing illegal migration across the Southwest
border remained a low priority during most of the 20th century.13
Illegal migration from Mexico increased after 1965 as legislative changes restricted legal
Mexican immigration at the same time that social and economic changes caused stronger
migration “pushes” in Mexico (e.g., inadequate employment opportunities) and stronger “pulls”
in the United States (e.g., employment opportunities, links to migrant communities in Mexico).14
Congress held hearings on illegal immigration beginning in 1971, and after more than a decade of
debate passed the Immigration Reform and Control Act of 1986 (IRCA, P.L. 99-603), which
described border enforcement as an “essential element” of immigration control and authorized a
9 See, for example, Alan Gomez, “Border Security Quandary Could Kill Immigration Bill,” USA Today, April 2, 2013.
10 Act of May 28, 1924; (43 Stat. 240).
11 Immigration Act of May 26, 1924 (43 Stat. 153).
12 See U.S. Customs and Border Protection (CBP), “Border Patrol History,” http://www.cbp.gov/xp/cgov/
border_security/border_patrol/border_patrol_ohs/history.xml.
13 See Kitty Calavita, Inside the State: The Bracero Program, Immigration, and the I.N.S. (New York: Routledge,
1992); Mark Reisler, By the Sweat of Their Brow: Mexican Immigrant Labor in the United States, 1900-1940
(Westport, CT: Greenwood Press, 1976); Douglas S. Massey, Jorge Durand, and Nolan J. Malone, Beyond Smoke and
Mirrors: Mexican Immigration in an Era of Economic Integration (New York: Russell Sage Foundation, 2002).
14 See CRS Report R42560, Mexican Migration to the United States: Policy and Trends, coordinated by Ruth Ellen
Wasem. Legislative changes included the termination of the U.S.-Mexican Bracero guest worker program in 1965 and
the imposition of numeric limits on migration from Mexico and other Western Hemisphere countries pursuant to the
Immigration and Nationality Act Amendments of 1965 (P.L. 89-236).
Congressional Research Service
2
Border Security: Immigration Enforcement Between Ports of Entry
50% increase in funding for the Border Patrol, among other provisions.15 Congress passed at least
11 additional laws addressing illegal immigration over the next two decades, 7 of which included
provisions related to the border.16
Border Patrol Strategic Plans
Seventy years after it began operations, the Border Patrol developed its first formal national
border control strategy in 1994, the National Strategic Plan. The plan was updated in 2004 and
again in 2012.
National Strategic Plan
The National Strategic Plan (NSP) was developed in 1994 in response to a widespread perception
that the Southwest border was being overrun by unauthorized immigration and drug smuggling,
and to respond to a study commissioned by the Office of National Drug Control Policy. The study
recommended that the INS change its approach from arresting unauthorized immigrants after they
enter the United States, as had previously been the case, to focus instead on preventing their
entry.17 Under the new approach, the INS would place personnel, surveillance technology,
fencing, and other infrastructure directly on the border to discourage illegal flows, a strategy that
became known as “prevention through deterrence.” According to the 1994 INS plan, “the
prediction is that with traditional entry and smuggling routes disrupted, illegal traffic will be
deterred, or forced over more hostile terrain, less suited for crossing and more suited for
enforcement.”18
The strategy had four phases that began with the border patrol sectors with the highest levels of
illegal immigration activity.
• Phase I: San Diego, CA, and El Paso, TX, sectors;
• Phase II: Tucson, AZ, Del Rio, TX, Laredo, TX, and McAllen, TX, sectors;
• Phase III: El Centro, CA, Yuma, AZ, and Marfa, TX, sectors; and
• Phase IV: The northern border, gulf coast, and coastal waterways.
The strategy yielded several initiatives aimed at stemming illegal immigration and human
smuggling, and interdicting drug trafficking. These initiatives included the following:
15 See U.S. Congress, House Committee on the Judiciary, The “Immigration Reform and Control Act of 1986” (P.L.
99-603), 99th Cong., 2nd Sess., December 1986, H. Rept. 99-14 (Washington: GPO, 1986).
16 The seven laws that included border-related provisions were the Immigration Act of 1990 (P.L. 101-649), the Illegal
Immigration Reform and Immigrant Responsibility Act of 1996 (P.L. 104-208, Div. C), the USA-PATRIOT Act of
2002 (P.L. 107-56), the Homeland Security Act of 2002 (P.L. 107-296), the Intelligence Reform and Terrorism
Prevention Act of 2004 (108-458), the REAL-ID Act of 2005 (P.L. 109-13, Div. B), and the Secure Fence Act of 2006
(P.L. 109-367).
17 U.S. Office of National Drug Control Policy, National Drug Control Strategy: Reclaiming Our Communities from
Drugs and Violence (Washington, DC: U.S. Department of Justice, 1994), https://www.ncjrs.gov/pdffiles1/ondcp/
150489.pdf.
18 U.S. Border Patrol, Border Patrol Strategic Plan: 1994 and Beyond, July 1994, pp. 6-7 (Hereinafter, National
Strategic Plan).
Congressional Research Service
3
Border Security: Immigration Enforcement Between Ports of Entry
• Operation Gatekeeper was first initiated at the San Diego Border Patrol Sector
and was later extended to the El Centro Border Patrol Sector. The initiative
involved providing border patrol agents with additional resources, such as
increased staffing and new technologies.
• Operation Safeguard was initiated at the Tucson Border Patrol Sector and was
aimed at stemming illegal immigration by pushing illegal immigrants away from
urban areas.
• Operation Hold the Line was initiated at the El Paso Border Patrol Sector and
was aimed at the specific needs of the community. New border patrol agents were
added to the area and innovative resources were deployed, including IDENT19
terminals. The initiative also included the installation of fences along parts of the
border and other infrastructure improvements.
• Operation Rio Grande was initiated at the McAllen Border Patrol Sector and
focused on increasing the number of border patrol agents.
The implementation of Phase II and subsequent phases was to be based on the success of Phase I,
with the plan describing several expected indicators of effective border enforcement, including an
initial increase of border arrests and entry attempt to be followed by an eventual reduction of
arrests, a change in traditional traffic patterns, and an increase in more sophisticated smuggling
methods.20 As predicted, apprehensions within the San Diego and El Paso sectors fell sharply
beginning in 1994-1995, and traffic patterns shifted, primarily to the Tucson and South Texas
(Rio Grande Valley) sectors (see “Southwest Border Apprehensions by Sector”). A 1997 General
Accounting Office (GAO) report was cautiously optimistic about the strategy.21
Congress supported the prevention through deterrence approach. In 1996, House and Senate
appropriators directed the INS to hire new agents and to reallocate personnel from the interior to
front line duty.22 And the Illegal Immigration Reform and Immigrant Responsibility Act of 1996
(P.L. 104-208) expressly authorized the construction and improvement of fencing and other
barriers along the Southwest border and required the completion of a triple-layered fence along
14 miles of the border near San Diego where the INS had begun to install fencing in 1990.23
National Border Patrol Strategy
In the wake of the September 11, 2001, terrorist attacks, the USBP refocused its priorities on
preventing terrorist penetration, while remaining committed to its traditional duties of preventing
19 The Automated Biometric Identification (IDENT) system is DHS’s primary biometric database. Certain aliens’
biometric records are added to IDENT upon admission to the United States, when aliens are apprehended or arrested by
a DHS agency, and when aliens apply for certain immigration benefits.
20 National Strategic Plan, pp. 9-10.
21 U.S. General Accountability Office, Illegal Immigration: Southwest Border Strategy Results Inconclusive; More
Evaluation Needed, GAO/GGD-98-21, December 1997.
22 U.S. Congress, Senate Committee on Appropriations, Departments of Commerce, Justice, and State, The Judiciary,
and Related Agencies Appropriations Bill, 1996, report to accompany H.R. 2076, 104th Cong., 1st sess., S.Rept. 104-
139 and U.S. Congress, House Committee on Appropriations, Making Appropriations for the Departments of
Commerce, Justice, and State, The Judiciary, and Related Agencies For the Fiscal Year Ending September 30, 1996,
and for Other Purposes, report to accompany H.R. 2076, 104th Cong., 1st sess., H.Rept. 104-378.
23 P.L. 104-208, Div. C §102.
Congressional Research Service
4
Border Security: Immigration Enforcement Between Ports of Entry
the illicit trafficking of people and contraband between official ports of entry. Shortly after the
creation of DHS, the USBP was directed to formulate a new National Border Patrol Strategy
(NBPS) that would better reflect the realities of the post-9/11 security landscape. In March 2004,
the Border Patrol unveiled the National Border Patrol Strategy, which placed greater emphasis on
interdicting terrorists and featured five main objectives:
• establishing the substantial probability of apprehending terrorists and their
weapons as they attempt to enter illegally between the ports of entry;
• deterring illegal entries through improved enforcement;
• detecting, apprehending, and deterring smugglers of humans, drugs, and other
contraband;
• leveraging “Smart Border” technology to multiply the deterrent and enforcement
effect of agents; and
• reducing crime in border communities, thereby improving the quality of life and
economic vitality of those areas.24
The NBPS was an attempt to lay the foundation for achieving “operational control” over the
border, defined by the Border Patrol as “the ability to detect, respond, and interdict border
penetrations in areas deemed as high priority for threat potential or other national security
objectives.”25 The strategy emphasized a hierarchical and vertical command structure, featuring a
direct chain of command from headquarters to the field. The document emphasized the use of
tactical, operational, and strategic intelligence and sophisticated surveillance systems to assess
risk and target enforcement efforts; and the rapid deployment of USBP agents to respond to
emerging threats. Additionally, the plan called for the Border Patrol to coordinate closely with
CBP’s Office of Intelligence and other federal intelligence agencies.
Border Patrol Strategic Plan
CBP published a new Border Patrol Strategic Plan (BPSP) in May 2012 that shifted attention
from resource acquisition and deployment to the strategic allocation of resources by “focusing
enhanced capabilities against the highest threats and rapidly responding along the border.”26 From
an operational perspective, the 2012 plan emphasizes the collection and analysis of information
about evolving border threats; integration of Border Patrol and CBP planning across different
border sectors and among the full range of federal, state, local, tribal, and international
organizations involved in border security operations; and rapid Border Patrol response to specific
border threats.27
24 Department of Homeland Security, Bureau of Customs and Border Protection, National Border Patrol Strategy,
March 1, 2005. Hereinafter, USBP National Strategy.
25 USBP National Strategy, p. 3. This definition differs from the statutory definition found in Section 2 of the Secure
Fence Act of 2006 (P.L. 109-367); see in this report “Operational Control of the Border.”
26 CBP, 2012-2016 Border Patrol Strategic Plan, Washington, DC: 2012, p. 7.
27 Ibid.
Congressional Research Service
5
Border Security: Immigration Enforcement Between Ports of Entry
DHS Secure Border Initiative
The Border Patrol’s approach to border enforcement has been mirrored in broader DHS policies.
In November 2005, the Department of Homeland Security announced a comprehensive multi-
year plan, the Secure Border Initiative (SBI), to secure U.S. borders and reduce illegal
migration.28 Under SBI, DHS announced plans to obtain operational control of the northern and
southern borders within five years by focusing attention in five main areas:
• Increased staffing. As part of SBI, DHS announced the addition of 1,000 new
Border Patrol agents, 250 new ICE investigators targeting human smuggling
operations, and 500 other new ICE agents and officers.29
• Improved detention and removal capacity. Historically, most non-Mexicans
apprehended at the border were placed in formal removal proceedings.30 Yet
backlogs in the immigration court system meant that most such aliens were
released on bail or on their own recognizance prior to a removal hearing, and
many failed to show up for their hearings.31 In October 2005, DHS announced
plans to detain 100% of non-Mexicans apprehended at the border until they could
be processed for removal. SBI supported this goal by adding detention capacity,
initially increasing bed space by 2,000 to a total of 20,000.32 On August 23, 2006,
DHS announced that the policy to “end catch and release” had been successfully
implemented.33
• Surveillance technology. SBI included plans to expand DHS’s use of
surveillance technology between ports of entry, including unmanned aerial
vehicle (UAV) systems, other aerial assets, remote video surveillance (RVS)
systems, and ground sensors.34 These tools were to be linked into a common
integrated system that became known as SBInet (see “Surveillance Assets”
below).
• Tactical infrastructure. SBI continued DHS’s commitment to the expansion of
border fencing, roads, and stadium-style lighting.35
28 DHS, “Fact Sheet: Secure Border Initiative,” https://www.hsdl.org/?view&did=440470.
29 Ibid.
30 Prior to 1996, the INA included distinct provisions for the “exclusion” of inadmissible aliens and the “deportation”
of certain aliens from within the United States. Pursuant to §§301-309 of the Illegal Immigration Reform and
Immigrant Responsibility Act of 1996 (IIRIRA, P.L. 104-208, Div. C), deportation and exclusion proceedings were
combined into a unified “removal” proceeding (8 U.S.C. 1229a). This report uses “deportation” to refer to the
compulsory return of aliens to their country of origin prior to the implementation of IIRIRA in 1997, and “removal” to
refer to aliens returned under these provisions since 1997.
31 DHS estimated that there were 623,292 alien “absconders” in August 2006, many of whom had failed to appear for
removal hearings after being apprehended at the border; see Doris Meissner and Donald Kerwin, DHS and
Immigration: Taking Stock and Correcting Course, Migration Policy Institute, Washington, DC, February 2009, p. 44,
http://www.migrationpolicy.org/pubs/DHS_Feb09.pdf.
32 DHS, “Fact Sheet: Secure Border Initiative,” https://www.hsdl.org/?view&did=440470.
33 CBP, “DHS Secretary Announces End to ‘Catch and Release’ on Southern Border,” http://www.cbp.gov/xp/cgov/
admin/c1_archive/messages/end_catch_release.xml.
34 DHS, “Fact Sheet: Secure Border Initiative,” https://www.hsdl.org/?view&did=440470.
35 Ibid.
Congressional Research Service
6
Border Security: Immigration Enforcement Between Ports of Entry
• Interior enforcement. SBI also included plans to expand enforcement within the
United States at worksites and through state and local partnerships, jail screening
programs, and task forces to locate fugitive aliens.36
CBP Consequence Delivery System
Although not the subject of a formal public policy document like those discussed above, an
additional component of CBP’s approach to border control in recent years has been an effort to
promote “high consequence” enforcement for unauthorized Mexicans apprehended at the border.
Historically, immigration agents permitted most Mexicans apprehended at the border to
voluntarily return to Mexico without any penalty.37 Since 2005, CBP has limited voluntary returns
in favor of three types of “high consequence” outcomes:
• Formal Removal.38 Aliens39 formally removed from the United States generally
are ineligible for a visa (i.e., inadmissible) for at least five years,40 and they may
be subject to criminal charges if they illegally reenter the United States.41 Prior to
2005, most unauthorized Mexicans apprehended at the border were not placed in
removal proceedings, in part because standard removal procedures require an
appearance before an immigration judge and are resource intensive. 42 Since
2005, CBP has relied extensively on two provisions in the Immigration and
Nationality Act (INA) that permit aliens to be formally removed with limited
judicial processing. Under INA Section 235(b), certain arriving aliens are subject
to “expedited removal” (ER) without additional hearing or review.43 ER was
added to the INA in 1996, but initially was reserved for aliens apprehended at
ports of entry. In a series of four announcements between November 2002 and
January 2006, DHS expanded the use of ER to include certain aliens who had
entered the United States within the previous two weeks and who were
apprehended anywhere within 100 miles of a U.S. land or coastal border.44 Under
INA Section 241(a)(5), an alien who reenters the United States after being
36 Ibid. Interior enforcement programs are not discussed in this report; see CRS Report R42057, Interior Immigration
Enforcement: Programs Targeting Criminal Aliens, by Marc R. Rosenblum and William A. Kandel; and CRS Report
R40002, Immigration-Related Worksite Enforcement: Performance Measures, by Andorra Bruno.
37 Section 240B of the INA permits immigration agents and judges to allow certain removable aliens to “voluntarily
depart” the United States. In contrast with aliens subject to formal removal, aliens subject to voluntary departure
generally do not face additional immigration-related penalties.
38 Pursuant to §§301-309 of the Illegal Immigration Reform and Immigrant Responsibility Act of 1996 (IIRIRA, P.L.
104-208, Div. C), deportation and exclusion proceedings were combined into a unified “removal” proceeding (INA
§240); and immigration judges were given discretion to permit aliens who are subject to removal to “voluntarily
depart” in lieu of facing formal removal proceedings (INA §240B).
39 “Aliens” is synonymous with non-citizens, including legal permanent residents, temporary nonimmigrants, and
unauthorized aliens.
40 INA §212(a)(9).
41 INA §276.
42 Most non-Mexican aliens, however, were placed in formal removal proceedings and, after 2005, were normally
detained until a removal order was implemented (see in this report “DHS Secure Border Initiative”).
43 Aliens who indicate an intention to apply for asylum or a fear of persecution are not subject to formal removal; for a
fuller discussion of expedited removal see archived CRS Report RL33109, Immigration Policy on Expedited Removal
of Aliens, by Alison Siskin and Ruth Ellen Wasem.
44 Ibid. Under the 2006 policy, most Mexicans apprehended at the Southwest border were not placed in expedited
removal proceedings unless they had previous criminal convictions.
Congressional Research Service
7
Border Security: Immigration Enforcement Between Ports of Entry
formally removed or departing under a removal order is subject to “reinstatement
of removal” without reopening or reviewing the original removal order.45
• Criminal Charges. Unauthorized aliens apprehended at the border may face
federal immigration charges,46 but historically, most such aliens have not been
charged with a crime. Working with the Department of Justice (DOJ), DHS has
increased the proportion of people apprehended at the border who are charged
with immigration-related criminal offenses. A portion of aliens facing criminal
charges in Southwest border districts are prosecuted through the “Operation
Streamline” program (see accompanying text box). Mexicans apprehended in the
United States who are found to be smuggling aliens may also be subject to
criminal charges in Mexico under the U.S.-Mexican Operation Against
Smugglers Initiative on Safety and Security (OASISS).47
Operation Streamline
Operation Streamline is a partnership program among CBP, U.S. Attorneys, and District Court judges in certain
border districts to expedite criminal justice processing. The program permits groups of criminal defendants to have
their cases heard at the same time, rather than requiring judges to review individual charges, and arranges in most
cases for aliens facing felony charges for illegal re-entry to plead guilty to misdemeanor illegal entry charges—a plea
bargain that leads to the rapid resolution of cases. Although Operation Streamline has been described as a zero
tolerance program leading to prosecutions for 100% of apprehended aliens, the program confronts limits in judicial
and detention capacity, resulting in daily caps on the number of people facing charges in certain districts. In the
Tucson sector, for example, the courts reportedly limit Streamline cases to about 70 prosecutions per day.
Operation Streamline was established in the USBP’s Del Rio Sector in December 2005 and expanded to the Yuma
Sector in December 2006, Laredo Sector in October 2007, Tucson Sector in January 2008, and Rio Grande Val ey
Sector in June 2008. The program mainly consists of procedural arrangements among DHS and DOJ officials at the
local level, and 15 CBP agents have been detailed to DOJ in three Border Patrol sectors to assist DOJ attorneys and
U.S. Marshal s with prosecutions. A total of 208,939 people were processed through Operation Streamline through
the end of FY2012—about 45% of the 463,051 immigration-related prosecutions in Southwest border districts during
this period.
On October 17, 2014, House Judiciary Committee Chairman Goodlatte issued a press release that included the text
of a letter he sent to Attorney General Eric Holder. In the letter, Chairman Goodlatte expressed concern over the
decrease in the number of prosecutions under Operation Streamline for first-time illegal border crossers. According
to the Yuma County (AZ) Sheriff, the U.S. Attorney’s Office for the District of Arizona will cease prosecuting first-
time illegal border crossers, and only undocumented aliens with an adverse immigration history (not including aliens
who were processed under voluntary return and voluntary departure) will be prosecuted under immigration law.
Sources: CBP Office of Congressional Affairs; National Research Council Committee on Estimating Costs of
Immigration Enforcement in the Department of Justice, Budgeting for Immigration Enforcement: A Path to Better
Performance (Washington, DC: National Academies Press, 2011); House Judiciary Committee, Chairman Bob
Goodlatte, “Goodlatte Seeks Answers About the Drop in the Number of Prosecutions for First-Time Illegal Border
Crossers,” press release, Oct. 17, 2014; and Yuma County Sheriff’s Office, letter to Senator Jeff Flake, Aug. 19, 2014.
45 CBP’s expanded use of reinstatement of removal depended, in part, on its ability to identify repeat offenders by
enrolling their biometric data in the Automated Biometric Identification System (IDENT) system, a database of over
150 million individual records. For a fuller discussion of the US-VISIT system see CRS Report R43356, Border
Security: Immigration Inspections at Ports of Entry, by Lisa Seghetti.
46 Aliens apprehended at the border may face federal immigration-related criminal charges for illegal entry (8 U.S.C.
§1325) or (on a second or subsequent apprehension) illegal re-entry (8 U.S.C. §1326), and in some cases they may face
charges related to human smuggling (8 U.S.C. §1324) and visa and document fraud (18 U.S.C. §1546), among other
charges. Unlawful presence in the United States absent additional factors, however, is a civil violation, not a criminal
offense. See CRS Report RL32480, Immigration Consequences of Criminal Activity, by Michael John Garcia.
47 A total of about 3,000 people were transferred to Mexico for prosecution under the program in FY2005-FY2012,
according to data provided to CRS by CBP Office of Congressional Affairs.
Congressional Research Service
8
Border Security: Immigration Enforcement Between Ports of Entry
• Remote repatriation. CBP uses a pair of programs to return Mexicans to remote
locations rather than to the nearest Mexican port of entry. Under the Alien
Transfer Exit Program (ATEP), certain Mexicans apprehended near the border
are repatriated to border ports hundreds of miles away—typically moving people
from Arizona to Texas or California—a process commonly described as “lateral
repatriation.”48 Under the Mexican Interior Repatriation Program (MIRP), certain
Mexican nationals are repatriated to their home towns within Mexico rather than
being returned just across the border.49
In general, these high consequence enforcement outcomes are intended to deter illegal flows by
raising the costs to migrants of being apprehended and by making it more difficult for them to
reconnect with smugglers following a failed entry attempt.50 To manage these disparate programs,
CBP has designed the “Consequence Delivery System.... to uniquely evaluate each subject [who
is apprehended] and identify the ideal consequences to deliver to impede and deter further illegal
activity.”51 USBP agents use laminated cards with matrices describing the range of enforcement
actions available for a particular alien as a function of the person’s immigration and criminal
histories, among other factors, and of the enforcement resources available in each Border Patrol
sector. According to public comments by then CBP Commissioner Alan Bersin, the goal of the
Consequence Delivery System, in certain sectors of the border, is to ensure that virtually
everyone who is apprehended faces “some type of consequence” other than voluntary return.52
As Figure 1 indicates, the effort to limit voluntary returns in favor of “high consequence”
enforcement outcomes has, to a great degree, been implemented. The figure depicts Southwest
border apprehensions (the solid line) and the four main types of enforcement outcomes (voluntary
returns, criminal charges, formal removal, and remote repatriation—the shaded areas) for
FY2005-FY2012.53 (Enforcement outcomes exceed apprehensions because some aliens face more
than one outcome, such as formal removal along with lateral repatriation. In addition, certain
aliens apprehended in one fiscal year do not complete their case processing until the following
year.) As the figure illustrates, voluntary return fell from 77% of all enforcement outcomes in
2005 (956,470 out of 1,238,554) to 14% in FY2012 (76,664 out of 529,393). Conversely, the
proportion of enforcement outcomes that were high consequence outcomes (i.e., criminal charges,
48 See U.S. Congress, House Committee on Homeland Security, Subcommittee on Border and Maritime Security, Does
Administrative Amnesty Harm our Efforts to Gain and Maintain Operational Control of the Border, testimony of U.S.
Border Patrol Chief Michael J. Fisher, 112th Cong., 1st sess., October 4, 2011.
49 Ibid.
50 See U.S. Congress, House Committee on Homeland Security, Subcommittee on Border and Maritime Security, Does
Administrative Amnesty Harm our Efforts to Gain and Maintain Operational Control of the Border, testimony of U.S.
Border Patrol Chief Michael J. Fisher, 112th Cong., 1st sess., October 4, 2011. Most alien smugglers reportedly charge
aliens a set fee to enter the United States regardless of the number of attempts, so one goal of the high consequence
enforcement programs is to disrupt smugglers’ business model.
51 Ibid. The Consequence Delivery System was formally launched January 1, 2011.
52 Alan Bersin, The State of US/Mexico Border Security, Center for American Progress, August 4, 2011. Under section
240B of the Immigration and Nationality Act (INA), immigration officers and/or immigration judges may permit
certain aliens to depart the United States in lieu of (or at the termination of) a formal removal hearing, a process known
as “voluntary departure” or “voluntary return.” Bersin indicated that certain aliens may still be eligible for voluntary
return, such as aliens younger than 18 years old traveling without a parent or legal guardian (i.e., unaccompanied
minors).
53 CRS attempted to obtain more current data (i.e., FY2013 and FY2014); however, according to DHS the data are not
available for release. CRS email with DHS Congressional Affairs office on November 13, 2014.
Congressional Research Service
9
Border Security: Immigration Enforcement Between Ports of Entry
formal removal, or remote repatriation) increased from 23% (282,084 out of 1,238,554) in
FY2005 to 86% in FY2012 (452,664 out of 529,393).
Figure 1. CBP “Enforcement with Consequences,” FY2005-FY2012
Southwest Border
Sources: CRS presentation of data provided by CBP Office of Congressional Affairs March 10, 2013; ICE Office
of Congressional Affairs March 22, 2013; Administrative Office of the U.S. Courts.
Notes: Immigration-related criminal charges may include some U.S. citizens and lawful aliens.
One factor that has facilitated the rise in the proportion of apprehensions subject to high-
consequence enforcement has been a sharp drop in the number of aliens apprehended on the
Southwest border, as discussed in this report (see “Alien Apprehensions”). Nonetheless, as
Figure 1 also illustrates, CBP’s effort to expand high-consequence enforcement has resulted in a
rise in removals, prosecutions, and lateral/interior repatriations since 2007, even during a period
of falling border apprehensions.
With the implementation of the Consequence Delivery System, the Border Patrol has initiated a
system to estimate the deterrent effect of different enforcement outcomes. In particular, the
Border Patrol tracks, for each of 10 different enforcement consequences, the percentage of aliens
who were re-apprehended during the same fiscal year following repatriation (i.e., the recidivism
rate). These recidivism rates are reported in Table 1.54
54 CRS attempted to obtain more current data (i.e., FY2013 and FY2014); however, according to DHS the data are not
available for release. CRS email with DHS Congressional Affairs office on November 13, 2014.
Congressional Research Service
10
Border Security: Immigration Enforcement Between Ports of Entry
Table 1. Consequence Delivery System Outcomes and Recidivism Rates
Southwest Border
FY2011
FY2012
Consequence
Number of
Recidivism
Number of
Recidivism
Cases
Rate
Cases
Rate
Criminal
OASISS
533 14.7% 429 10.2%
Charges
Operation
Streamline 36,871 12.1% 44,300 10.3%
Standard
Prosecution 31,130 9.1%
34,839 9.1%
Formal
Notice to Appear
20,923
6.6%
23,491
3.8%
Removal
Expedited
Removal 39,855 16.6%
148,548 16.4%
Reinstatement
74,106 16.9% 98,424 15.9%
Quick
Court
2,730 19.0% 1,070 18.3%
Remote
MIRP 8,940
9.3%
0
NAa
Repatriation
ATEP
75,966 27.8%
101,992 23.8%
Voluntary
Return
129,207 29.4% 76,664 27.1%
Total
Cases
318,883 19.8%
347,921 16.7%
Source: CRS analysis based on data provided by CBP Office of Congressional Affairs, March 10, 2013.
Notes: OASISS stands for the U.S.-Mexican Operation Against Smugglers Initiative on Safety and Security. See
text for discussions of Operation Streamline, expedited removal, and reinstatement of removal. Standard
Prosecution refers to criminal charges through the standard federal prosecution process. Notice to appear is the
first stage in the standard formal removal process before an immigration judge. Quick court is a program
involving expedited removal hearings before an immigration judge. MIRP stands for the Mexico Interior
Repatriation Program. ATEP stands for the Alien Transfer Exchange Program. Total Cases refers to the total
number of apprehensions and border-wide overall recidivism rate. The sum of the consequences exceeds the
number of total cases because some people are subject to more than one consequence.
a. MIRP did not operate in FY2012.
As Table 1 indicates, several consequences were associated with recidivism rates well below the
overall FY2012 average of 16.7%. These low recidivism consequences included standard
removal proceedings following a notice to appear (3.8%), standard criminal prosecutions (9.1%),
criminal charges through the OASISS program (10.2%), and Operation Streamline (10.3%).
Recidivism rates were also lower than the FY2011 average of 19.8% for aliens returned to
Mexico through the MIRP program (9.3%) in that year. (MIRP did not operate in FY2012.)
Conversely, recidivism rates in FY2012 were well above the overall average for aliens subject to
voluntary return (27.1%) and for aliens subject to lateral repatriation through the ATEP program
(23.8%).55
The differences in recidivism rates may not be wholly attributable to differences among the
consequences because the Border Patrol takes account of aliens’ migration histories and other
factors when assigning people to different enforcement outcomes. Nonetheless, these data suggest
that standard removal and criminal charges have a stronger deterrent effect on future unauthorized
55 CRS attempted to obtain more current data (i.e., FY2013 and FY2014); however, according to DHS the data are not
available for release. CRS email with DHS Congressional Affairs office on November 13, 2014.
Congressional Research Service
11
Border Security: Immigration Enforcement Between Ports of Entry
migration than does voluntary return. Conversely, lateral repatriation appears to do little to
discourage people from reentering the United States.56
Southern Border Campaign Plan57
In a November 20, 2014, memo, Secretary Johnson “commissions” three Joint Task Forces.58
According to Secretary Johnson, the three Joint Task Forces will bring together personnel from
CBP as well as other DHS agencies—U.S. Coast Guard (USCG), U.S. Immigration and Customs
Enforcement (ICE), and U.S. Citizenship and Immigration Services (USCIS). The Joint Task
Forces will also “integrate capabilities of the remaining [DHS] components as needed.”59
According to Secretary Johnson, “Two of these task forces will be geographically based and one
will be functionally focused.”60 Joint Task Force East will cover “the Southern maritime border
and approaches.”61 Joint Task Force West will have responsibility for the southern land border
and the West Coast, while an entity dubbed Joint Task Force Investigations “will focus on
investigations in support of the geographic Task Forces.”62 The memo lays out broad missions
and objectives and sets a 90-day timeframe to “realign personnel and stand up headquarters
capabilities within each Joint Task Force.”63
Budget and Resources
Statutory and strategic changes since 1986 are reflected in border enforcement appropriations and
in CBP’s assets at the border, including personnel, infrastructure, and surveillance technology.
This section reviews trends in each of these areas.
Border Security Appropriations
Figure 2 depicts U.S. Border Patrol appropriations for FY1989-FY2013. Appropriations have
grown steadily over this period, rising from $232 million in 1989 to $1.3 billion in FY2002 (the
last data available prior to the creation of DHS), $3.8 billion in FY2010, and $3.7 billion in
FY2014.64 The largest growth came following the formation of DHS in FY2003, reflecting
Congress’s focus on border security in the aftermath of 9/11.
56 According to CBP Office of Congressional Affairs (April 24, 2013), aliens repatriated through the Alien Transfer
Exit Program (ATEP) typically are voluntarily returned or subject to expedited removal. Thus, ATEP’s high recidivism
rates are partly a result of the relatively high rates associated with these two outcomes.
57 This section was authored by Jerome Bjelopera, Specialist in Organized Crime and Terrorism.
58 Memo from Jeh Charles Johnson, Secretary, Department of Homeland Security, to R. Gil Kerlikowske,
Commissioner, U.S. Customs and Border Protection, et al., November 20, 2014.
59 Ibid.
60 Ibid.
61 Ibid.
62 Ibid.
63 Ibid.
64 See Figure 2 for sources. Due to the manner in which the Border Patrol collects and organizes its data, all statistics
presented in this report (except where otherwise indicated) are based on the federal fiscal year, which begins October 1
and ends on September 30. All dollar amounts in this report are nominal values for the year from which data are
reported.
Congressional Research Service
12
Border Security: Immigration Enforcement Between Ports of Entry
Figure 2. U.S. Border Patrol Appropriations, FY1989-FY2014
Sources: INS Congressional Budget Justification FY1991-FY2002; DHS Appropriations reports FY2004-FY2014.
Notes: Appropriations for 1989-2002 reflect the “Border Patrol” sub-account of the INS Salaries and Expenses
account of the DOJ annual appropriations. Appropriations for 2004-2014 reflect the “Border Security and
Control between Ports of Entry” sub-account of the CBP Salaries and Expenses account of the DHS annual
appropriations. Data are not available for FY2003 because neither the INS nor congressional appropriators
provided a breakout of the salaries and expenses sub-accounts within the Enforcement and Border Affairs
account during that year’s funding cycle. The overall Enforcement and Border Affairs account within INS for
FY2003 was $2,881 million, up from $2,541 million in FY2001 and $2,740 million in FY2002. With the
establishment of DHS, the former INS, customs inspections from the former U.S. Customs Service, and the U.S.
Border Patrol were merged to form the Bureau of Customs and Border Protection within DHS. As a result, data
for years prior to FY2003 may not be strictly comparable with data for FY2004 and after. FY2005 figure includes
a $124 million supplemental appropriation from P.L. 109-13. FY2006 figure does not include any portion of the
$423 million in supplemental funding for CBP Salaries and Expenses in P.L. 109-234 because the law did not
specify how much of this funding was for USBP; DHS reported in its FY2008 DHS Budget Justification that the
Border Patrol received a $1,900 mil ion appropriation in FY2006. FY2010 figure includes a $176 mil ion
supplemental appropriation from P.L. 111-230. FY2013 figure includes the pre-sequester amount.
Appropriations reported in Figure 2 are only a subset of all border security funding. These data
do not include, for example, additional CBP sub-accounts funding Headquarters Management and
Administration ($1.2 billion in FY2014), and Border Security Inspections and Trade Facilitation
at Ports of Entry ($3.2 billion in FY2014); or additional CBP accounts funding Border Security
Fencing, Infrastructure, and Technology ($351 million in FY2014); Air and Marine Operations
Congressional Research Service
13
Border Security: Immigration Enforcement Between Ports of Entry
($805 million in FY2014) and Facilities Management ($456 million in FY2014).65 A substantial
portion of these accounts is dedicated to border security and immigration enforcement, as these
terms are commonly used. The data in Figure 2 also exclude U.S. Immigration and Customs
Enforcement (ICE) appropriations, which totaled $5.2 billion for Salaries and Expenses for
FY2014.66 About a quarter of ICE’s 20,000 personnel reportedly are deployed to the Southwest
border.67 And Figure 2 excludes border enforcement appropriations for other federal agencies—
including the Departments of Justice, Defense, the Interior, and Agriculture, all of which play a
role in border security—as well as funding for the U.S. federal court system.68
Border Patrol Personnel
Accompanying this budget increase, Congress has passed at least four laws since 1986
authorizing increased Border Patrol personnel.69 USBP staffing roughly doubled in the decade
after the 1986 IRCA, doubled again between 1996 and the 9/11 attacks, and doubled again in the
decade after 9/11 (see Figure 3). As of October 2014, the USBP had 20,833 agents, including
18,127 posted at the Southwest border.70
65 Account-level data are from the House Explanatory Statement to accompany P.L. 113-76. Also see CRS Report
R43417, Forest Service Appropriations, FY2010-FY2014: In Brief, by Katie Hoover.
66 Ibid.
67 Department of Homeland Security, “Secure and Manage Our Borders,” http://www.dhs.gov/xabout/
gc_1240606351110.shtm.
68 Over one-third of all federal criminal cases commenced in 2011-12 were for immigration cases; see U.S. Courts, U.S.
District Courts - Criminal Cases Commenced, by Offense, Washington, DC, 2011, http://www.uscourts.gov/uscourts/
Statistics/JudicialBusiness/2012/appendices/D02DSep12.pdf. The prosecution of these cases involves expenditures by
DOJ prosecutors, federal marshals, the federal bureau of prisons, and the U.S. district and magistrate court systems,
among others. The costs of border enforcement borne by federal law enforcement and judicial officials outside of DHS
are difficult to describe because these agencies do not list border-specific obligations in their budget documents. Also
see National Research Council Committee on Estimating Costs of Immigration Enforcement in the Department of
Justice, op. cit.
69 The Immigration Act of 1990 (P.L. 101-649) authorized an increase of 1,000 Border Patrol agents; the IIRIRA (P.L.
104-208, Div. C) authorized an increase of a total of 5,000 Border Patrol agents in FY1997-FY2001; the Uniting and
Strengthening America by Providing Appropriate Tools Required to Intercept and Obstruct Terrorism Act (USA
PATRIOT, P.L. 107-56) authorized INS to triple the number of Border Patrol agents at the northern border; and the
Intelligence Reform and Terrorism Prevention Act (P.L. 108-458) authorized an increase of 10,000 Border Patrol
agents between FY2006 and FY2010.
70 “Border Security in the 21st Century.”
Congressional Research Service
14
Border Security: Immigration Enforcement Between Ports of Entry
Figure 3. U.S. Border Patrol Agents, Total and by Region, FY1980-FY2013
Source: 1980-1991: CRS presentation of data from Syracuse University Transactional Records Access
Clearinghouse; 1992-2013: CRS presentation of data provided by CBP Office of Congressional Affairs.
Note: The total number of Border Patrol agents includes agents stationed in coastal sectors and at USBP
headquarters.
National Guard Troops at the Border
The National Guard also is authorized to support federal, state, and local law enforcement
agencies (LEAs) at the border. Basic authority for the Department of Defense (DOD, including
the National Guard) to assist LEAs is contained in Chapter 18 of Title 10 of the U.S. Code, and
DOD personnel are expressly authorized to maintain and operate equipment in cooperation with
federal LEAs in conjunction with the enforcement of counterterrorism operations or the
enforcement of counterdrug laws, immigration laws, and customs requirements.71 DOD may
assist any federal, state, or local LEA requesting counterdrug assistance under the National
Defense Authorization Act, as amended.72 Under Title 32 of the U.S. Code, National Guard
personnel also may serve a federal purpose, such as border security, and receive federal pay while
remaining under the command control of their respective state governors.73
National Guard troops were first deployed to the border on a pilot basis in 1988, when about 100
soldiers assisted the U.S. Customs Service at several Southwest border locations, and National
Guard and active military units provided targeted support for the USBP’s surveillance programs
throughout the following decade. The first large-scale deployment of the National Guard to the
border occurred in 2006-2008, when over 30,000 troops provided engineering, aviation,
identification, technical, logistical, and administrative support to CBP as part of “Operation Jump
71 See CRS Report R41286, Securing America’s Borders: The Role of the Military, by R. Chuck Mason.
72 P.L. 101-510. Div. A, Title X, §1004; also see Ibid.
73 32 U.S.C. §§502(a) and 502(f); also see CRS Report R41286, Securing America’s Borders: The Role of the Military,
by R. Chuck Mason.
Congressional Research Service
15
Border Security: Immigration Enforcement Between Ports of Entry
Start.”74 President Obama announced an additional deployment of up to 1,200 National Guard
troops to the Southwest border on May 25, 2010, with the National Guard supporting the Border
Patrol, by providing intelligence work and drug and human trafficking interdiction.75 The 2010
deployment was originally scheduled to end in June 2011, but the full deployment was extended
twice (in June and September 2011). The Administration announced in December 2011 that the
deployment would be reduced to fewer than 300 troops beginning in January 2012, with National
Guard efforts focused on supporting DHS’s aerial surveillance operations.76 In December 2012,
DHS and the Department of Defense announced that the National Guard deployment would be
extended through December 2013.77
Fencing and Tactical Infrastructure
Border tactical infrastructure includes roads, lighting, pedestrian fencing, and vehicle barriers.
Tactical infrastructure is intended to impede illicit cross-border activity, disrupt and restrict
smuggling operations, and establish a substantial probability of apprehending terrorists seeking
entry into the United States.78 The former INS installed the first fencing along the U.S.-Mexican
border beginning in 1990 east of the Pacific Ocean near San Diego.
Congress expressly authorized the construction and improvement of fencing and other barriers
under Section 102(a) of the Illegal Immigration Reform and Immigrant Responsibility Act of
1996 (IIRIRA),79 which also required the completion of a triple-layered fence along the original
14 mile border segment near San Diego. The Secure Fence Act of 200680 amended IIRIRA with a
requirement for double-layered fencing along five segments of the Southwest border, totaling
about 850 miles.81 IIRIRA was amended again by the Consolidated Appropriations Act, FY2008.
Under that amendment, the law now requires the Secretary of Homeland Security to construct
reinforced fencing “along not less than 700 miles of the southwest border where fencing would be
most practical and effective and provide for the installation of additional physical barriers, roads,
lighting, cameras, and sensors to gain operational control of the southwest border.”82 The act
further specifies, however, that the Secretary of Homeland Security is not required to install
fencing “in a particular location along the international border of the United States if the
Secretary determines that the use or placement of such resources is not the most appropriate
74 See CRS Report R41286, Securing America’s Borders: The Role of the Military, by R. Chuck Mason.
75 Ibid.
76 Associated Press, “National Guard Troops at Mexico Border Cut to Fewer Than 300,” USA Today, December 20,
2011.
77 Homeland Security Today, “Pentagon Extends Deployment of National Guard in CBP Air Support Mission,”
December 7, 2012.
78 Customs and Border Protection, “Tactical Infrastructure: History and Purpose,” http://www.cbp.gov/xp/cgov/
border_security/ti/about_ti/ti_history.xml.
79 P.L. 104-208, Div. C
80 P.L. 109-367
81 P.L. 109-367 subsequently identified five specific stretches of the border where fencing was to be installed; CBP
Congressional Affairs provided CRS with this estimate of the total mileage covered by the law on September 25, 2006.
82 P.L. 110-161, Div. E, §564. Unlike under prior law, the Consolidated Appropriations Act, as enacted, does not
specify that reinforced fencing be “at least 2 layers.” See P.L. 104-208, Div. C, §102(b), as amended by P.L. 109-367,
§3.
Congressional Research Service
16
Border Security: Immigration Enforcement Between Ports of Entry
means to achieve and maintain operational control over the international border at such
location.”83
Figure 4. Tactical Infrastructure Appropriations and Miles of Border Fencing,
FY1996-FY2013
Sources: INS Congressional Budget Justifications FY2001-FY2003; DHS Congressional Budget Justifications
FY2005-2007; DHS Appropriations bills FY2007-FY2013.
Notes: In FY2003, immigration inspections from the former INS, customs inspections from the former U.S.
Customs Service, and USBP were merged to form the Bureau of Customs and Border Protection within DHS.
As a result, data for years prior to FY2003 may not be comparable with the data for FY2004 and after. Data for
FY1996-FY2002 include USBP construction and tactical infrastructure accounts. Construction account funding
has been used to fund a number of projects at the border, including fencing, vehicle barriers, roads, and USBP
stations and checkpoints. Funding for FY1998-FY2000 includes San Diego fencing as wel as fencing, light, and
road projects in El Centro, Tucson, El Paso, and Marfa. Data for FY2003-FY2006 include DHS construction and
tactical appropriations. Data for FY2007-FY2012 include total appropriations to CBP’s Border Security Fencing,
Infrastructure, and Technology (BSFIT) account. This account funds the construction of fencing, other
infrastructure such as roads and vehicle barriers, as well as border technologies such as cameras and sensors.
As of October 2014, DHS installed 352.7 miles of primary pedestrian fencing, 299 miles of
vehicle fencing (total of 651 miles), and 36.3 miles of secondary fencing. The Border Patrol
reportedly had identified a total of 653 miles of the border as appropriate for fencing and barriers
(i.e., 2 additional miles).84 Figure 4 summarizes annual appropriations for tactical infrastructure
(including surveillance technology) for FY1996-FY2014. Appropriations increased from $25
million in FY1996 to $298 million in FY2006, an 11-fold increase (8-fold when adjusting for
inflation), and then jumped to $1.5 billion in FY2007 as DHS created a new Border Security
Fencing, Infrastructure, and Technology (BSFIT) account and appropriated money to pay for the
border fencing mandate in the Secure Fence Act of 2006. BSFIT appropriations have fallen for
83 P.L. 110-161, Div. E, §564.
84 Testimony of DHS Secretary Janet Napolitano before the Senate Judiciary Committee, The Border Security,
Economic Opportunity, and Immigration Modernization Act, S. 744, 113th Cong., 1st sess., April 23, 2013.
Congressional Research Service
17
Border Security: Immigration Enforcement Between Ports of Entry
seven consecutive years (from FY2007 through FY2013); however, in FY2014 BSFIT
appropriations increased to $351 million (from $324 million from the previous fiscal year).
Surveillance Assets
The Border Patrol uses advanced technology to augment its agents’ ability to patrol the border.
USBP’s border surveillance system has its origins in the former Immigration and Naturalization
Service’s (INS’s) Integrated Surveillance Information System (ISIS), initiated in 1998. ISIS was
folded into a broader border surveillance system named the America’s Shield Initiative (ASI) in
2005, and ASI was made part of DHS’s Secure Border Initiative (SBI) the following year, with
the surveillance program renamed SBInet and managed under contract by the Boeing
Corporation.
Under all three of these names, the system consisted of a network of remote video surveillance
(RVS) systems (including cameras and infrared systems), and sensors (including seismic,
magnetic, and thermal detectors), linked into a computer network, known as the Integrated
Computer Assisted Detection (ICAD) database. The system was intended to ensure seamless
coverage of the border by combining the feeds from multiple cameras and sensors into one
remote-controlled system linked to a central communications control room at a USBP station or
sector headquarters. USBP personnel monitoring the control room screened the ICAD system to
re-position RVS cameras toward the location where sensor alarms were tripped. Control room
personnel then alerted field agents to the intrusion and coordinated the response.
All three of these systems struggled to meet deployment timelines and to provide USBP with the
promised level of border surveillance.85 DHS also faced criticism of ASI and SBInet for non-
competitive contracting practices, inadequate oversight of contractors, and cost overruns.86 DHS
Secretary Napolitano ordered a department-wide assessment of the SBInet technology project in
January 2010 and suspended the SBInet contract in March 2010.87 The review confirmed
SBInet’s history of “continued and repeated technical problems, cost overruns, and schedule
delays, raising serious questions about the system’s ability to meet the needs for technology along
the border.”88 DHS terminated SBInet in January 2011.
Under the department’s Arizona Surveillance Technology Plan, the Border Patrol deploys a mix
of different surveillance technologies designed to meet the specific needs of different border
regions. As of November 2012, deployed assets included 337 Remote Video Surveillance
85 See, for example, testimony of DHS Inspector General Richard L. Skinner before the House Homeland Security
Committee, Subcommittee on Management, Integration, and Oversight, New Secure Border Initiative, 109th Cong., 1st
sess., December 16, 2005; GAO, Secure Border Initiative: DHS Needs to Address Significant Risks in Delivering Key
Technology Investment, GAO-08-1086, September 22, 2008; and GAO, Secure Border Initiative: Technology
Deployment Delays Persist and the Impact of Border Fencing Has Not Been Assessed, GAO-09-896,
http://www.gao.gov/new.items/d09896.pdf.
86 See DHS Inspector General (DHS IG), Secure Border Initiative: DHS Needs to Address Significant Risks in
Delivering Key Technology Investment, DHS OIG-09-80, Washington, DC, June 2009; DHS IG, Controls Over SBInet
Program Cost and Schedule Could Be Improved, DHS OIG-10-96, Washington, DC, June 2010.
87 Testimony of CBP Assistant Commissioner Mark Borkowski before the House Committee on Homeland Security,
Subcommittee on Border and Maritime Security, After SBInet–The Future of Technology on the Border, 112th Cong.,
1st sess., March 15, 2011.
88 DHS, Report on the Assessment of the Secure Border Initiative Network (SBInet) Program, Washington, DC, 2010,
p. 1.
Congressional Research Service
18
Border Security: Immigration Enforcement Between Ports of Entry
Systems (RVSS) consisting of fixed daylight and infrared cameras that transmit images to a
central location (up from 269 in 2006), 198 short and medium range Mobile Vehicle Surveillance
Systems (MVSS) mounted on trucks and monitored in the truck’s passenger compartment (up
from zero in 2005) and 41 long range Mobile Surveillance Systems (MSS, up from zero in 2005),
12 hand-held agent portable medium range surveillance systems (APSS, up from zero in 2005),
15 Integrated Fixed Towers that were developed as part of the SBInet system (up from zero in
2005), and 13,406 unattended ground sensors (up from about 11,200 in 2005).89 According to
CBP officials, the department’s acquisitions strategy emphasizes flexible equipment and mobile
technology that permits USBP to surge surveillance capacity in a particular region, and off-the-
shelf technology in order to hold down costs and get resources on the ground more quickly.
Aerial and Marine Surveillance
In addition to these ground-based surveillance assets, CBP deploys manned and unmanned
aircraft as well as marine vessels to conduct surveillance. Air and marine vessels patrol regions of
the border that are inaccessible to other surveillance assets, with unmanned aerial systems (UAS)
deployed in areas considered too high-risk for manned aircraft or personnel on the ground.90 In
FY2012, CBP’s Office of Air and Marine deployed 19 types of aircraft and three classes of
marine vessels, for a total of 269 aircraft and 293 marine vessels operating from over 70
locations.91 The agency reported 81,045 flight hours (down from about 95,000 in FY2011) and
47,742 underway hours in marine vessels (down from about 133,000 in FY2011).92 As of
November 2012, CBP operated a total of 10 UAS up from zero in 2006, including 2 UAS on the
Northern border, 5 on the Southwest border, and 3 in the Gulf of Mexico.93 UAS accounted for
5,737 flight hours in FY2012, up from 4,406 hours in FY2011.94
With support from Department of Defense (DOD), CBP conducted an evaluation of two
unmanned aerostat (tethered blimp) systems during the summer of 2012: the Persistent Ground
Surveillance System (PGSS) and the Rapid Aerostat Initial Deployment (RAID). In addition,
CBP evaluated PGSS and RAID towers, which support aerostat deployment as well as ground-
based technologies. These two systems have been deployed by the military to conduct area
surveillance. As a result of the evaluation, CBP concluded that these systems could provide useful
89 2012 data from U.S. Border Patrol Office of Congressional Affairs November 8, 2012; FY2006 data from DHS
Congressional Budget Justification 2006; 2005 data from GAO, “Border Security: Key Unresolved Issues Justify
Reevaluation of Border Surveillance Technology Program,” GAO-06-295, February 2006.
According to a 2014 GAO report, in addition to the technology programs mentioned in the text, the plan also includes
the following technologies: Integrated Fixes Towers, Agent Portable Surveillance System, and Thermal Imaging
Devices. GAO Report to Congressional Requesters, “Arizona Border Surveillance Technology Plan: Additional
Actions Needed to Strengthen Management and Assess Effectiveness,” March 2014.
90 U.S. Congress, Senate Committee on the Judiciary, The Future of Drones in America: Law Enforcement and Privacy
Considerations, testimony of DHS Acting Officer for Civil Rights and Civil Liberties Tamara Kessler, 113th Congress,
1st sess., March 20, 2013.
91 CBP Office of Congressional Affairs, March 19, 2013.
92 Ibid.; and CBP Office of Air and Marine, 2011 Air and Marine Milestones and Achievements,” http://www.cbp.gov/
xp/cgov/border_security/am/operations/2011_achiev.xml.
93 Northern border UAS are based in Grand Forks, ND; Southwest border UAS are based in Sierra Vista, AZ (four
systems) and Corpus Christi, TX (one system); and maritime UAS are based in Corpus Christi, TX (one system) and in
Cape Canaveral, FL (two systems).
94 Ibid.
Congressional Research Service
19
Border Security: Immigration Enforcement Between Ports of Entry
support to CBP operations on the border; and CBP reportedly is working with DOD to identify
opportunities to transfer ownership of aerostats returning from overseas to CBP.95
Border Patrol Enforcement Data
For 90 years, the Border Patrol has recorded the number of deportable aliens apprehended in the
United States;96 and alien apprehensions remain the agency’s primary indicator of immigration
enforcement. The agency also collects several additional measures of immigration enforcement,
including unique apprehensions, alien recidivism, and estimated turn backs and got aways. These
enforcement outcomes provide insight into the state of the border, as discussed in this section, but
they confront certain limitations when it comes to estimating illegal border inflows (see “Metrics
of Border Security”).
Alien Apprehensions
Figure 5 depicts total USBP apprehensions of deportable and removable aliens for FY1960-
FY2012. Apprehensions are widely understood to be correlated with illegal flows, and the data in
Figure 5 reflect historical trends in unauthorized migration (see “Border Patrol History and
Strategy”). Thus, apprehensions were very low in the 1960s, but climbed sharply in the two
decades after 1965. Apprehensions reached an all-time high of 1.7 million in 1986 and again in
2000, and an average of more than 1.2 million apprehensions per year were recorded 1983-2006,
reflecting high levels of unauthorized migration throughout this period. As Figure 5 also
illustrates, apprehensions have fallen sharply since 2000, and particularly since 2006. The
340,252 apprehensions observed in 2011 were the lowest level since 1971, and the 364,768
apprehensions in 2012 were the second-lowest level since that time. Falling apprehensions likely
reflected fewer illegal inflows between 2006 and 2012, though the degree to which reduced
inflows were a result of effective enforcement versus other factors like the recent U.S. economic
downturn remains subject to debate (see “How Secure is the U.S. Border?”).
The overwhelming majority of apprehensions take place along the Southwest border. In FY2014,
the Border Patrol apprehended 479,377 aliens along this border, an increase of 64,980 from the
previous year.97 The majority of these apprehensions occurred in the Rio Grande Valley Sector
(see discussion below).
95 CBP Office of Congressional Affairs, March 21, 2013.
96 Deportable aliens located refer to Border Patrol apprehensions and ICE administrative arrests. Prior to 1952, data
refer to Border Patrol apprehensions.
97 “Border Security in the 21st Century.” The spike in apprehensions in FY2014 can be largely attributed to the
unaccompanied alien children crisis.
Congressional Research Service
20
Border Security: Immigration Enforcement Between Ports of Entry
Figure 5. Total USBP Apprehensions of Deportable Aliens, FY1960-FY2012
Source: U.S. Border Patrol.
Southwest Border Apprehensions by Sector
Figure 6 depicts apprehensions along the Southwest border for FY1992-FY2013, broken down
by certain Border Patrol sectors. The sector-specific apprehension pattern generally adheres to the
predictions of the 1994 National Strategic Plan. Increased enforcement in the El Paso and San
Diego sectors was associated with high apprehensions in those sectors during the early 1990s, and
then with falling apprehensions by the middle of the decade. Apprehensions in the San Diego and
El Paso sectors remained well below their early-1990s levels throughout the following decade—
findings that suggest border enforcement in those sectors has been broadly effective.
Congressional Research Service
21
Border Security: Immigration Enforcement Between Ports of Entry
Figure 6. U.S. Border Patrol Apprehensions of Deportable Aliens, Southwest Border,
by Selected Sectors, FY1992-FY2013
Source: USBP, Total Apprehensions by Southwest Border Sectors.
Falling apprehensions in San Diego and El Paso during the late 1990s initially were more than
offset by rising apprehensions in the Tucson, AZ, sector and other border locations, including the
Laredo and Del Rio, TX, sectors. Since FY2011, apprehensions in Tucson have fallen back to
their lowest level since 1993, but apprehensions in the Rio Grande Valley have increased, and
now account for more than a quarter of Southwest border apprehensions.98 Thus, since the
initiation of the prevention through deterrence approach in the mid-1990s, it appears that success
in San Diego and El Paso may have come at the expense of Tucson and other sectors.
Unique Subjects and Alien Recidivism
Overall apprehensions data record apprehension events, and therefore count certain individuals
more than once because they enter and are apprehended multiple times. Since 2000, the Border
Patrol also has tracked the number of unique subjects the agency apprehends per year by
analyzing biometric data (i.e., fingerprints and digital photographs) of persons apprehended.99 As
Figure 7 illustrates, trends in unique subjects apprehended are similar to total apprehensions:
98 As mentioned elsewhere in this report, the recent increase in apprehensions in the Rio Grande Valley sector can
largely be attributed to the UAC phenomenon.
99 Biometric data of persons apprehended are recorded in the Automated Biometric Identification System (IDENT)
system. When Border Patrol agents enter aliens’ biometric data in the IDENT system, the data are automatically
checked against DHS’ “recidivist” database, which is used to track repeat entrants, and its “lookout” database, which is
used to identify criminal aliens. US-VISIT workstations also are fully interoperable with the Federal Bureau of
Investigation’s (FBI) 10-print Integrated Automated Fingerprint Identification System (IAFIS), a biometric database
that includes data on criminal records and the Department of Defense’s (DOD) Automated Biometric Identification
System (ABIS), which contains national security data.
Congressional Research Service
22
Border Security: Immigration Enforcement Between Ports of Entry
falling from 2000-2003, climbing in 2004-2005, and then falling sharply from about 818,000 in
2005 to about 247,000 individuals in 2011, before climbing back to 284,000 in FY2012.100
Figure 7. USBP Southwest Border Unique Subjects and Recidivism Rates
FY2000-FY2012
Source: CRS presentation of data provided by CBP Office of Congressional Affairs, March 10, 2013.
Notes: Total apprehensions refer to the total number of USBP apprehensions in Southwest border sectors;
unique subjects refers to the number of different people apprehended based on biometric records. The recidivism
rate is the percentage of unique individuals apprehended two or more times in a given fiscal year.
Significantly, the gap between total and unique apprehensions has steadily narrowed, with unique
subjects representing 54%-55% of total apprehensions in 2000-2001, 65%-70% in 2002-2010,
and 75%-80% in 2011-2012. Put another way, each unique subject is being apprehended fewer
times, on average, with the aggregate average number of apprehensions per person apprehended
(i.e., total apprehensions divided by unique subjects) falling from 1.9 apprehensions per person in
2000 to 1.3 apprehensions per person in 2012.101
This trend is explained, in part, by the bars in Figure 7, which depict annual Southwest border
recidivism rates, which USBP has tracked since 2005. The Border Patrol defines the annual
recidivism rate as the percentage of unique subjects apprehended more than once in a given fiscal
year. A goal of the Consequence Delivery System has been to deter aliens from re-entering—that
is, to reduce recidivism. As Figure 7 illustrates, recidivism rates increased slightly between 2005
(25%) and 2007 (29%), but have fallen since that time, reaching 17% in 2012.
100 CRS attempted to obtain more current data (i.e., FY2013 and FY2014); however, according to DHS the data are not
available for release. CRS email with DHS Congressional Affairs office on November 13, 2014.
101 These calculations are based on aggregate data provided to CRS.
Congressional Research Service
23
Border Security: Immigration Enforcement Between Ports of Entry
Estimated “Got Aways” and “Turn Backs”
Border Patrol stations and sectors estimate the number of illegal entrants who successfully travel
to the U.S. interior and who USBP ceased pursuing, or “got aways.”102 Stations and sectors also
estimate “turn backs,” the number of people who illegally cross the border but then cross back to
Mexico. USBP uses the sum of got aways, turn backs, and apprehensions to estimate the total
number of known illegal entries (also see “Border Patrol Effectiveness Rate”). The agency has
used these data since 2006 to inform tactical decision making and to allocate resources across
Southwest border sectors, but the Border Patrol has not published them or viewed them as reliable
metrics of border security because of challenges associated with measuring got aways and turn
backs across different border sectors.103
Additional Border Security Data: Migrant Surveys
Apart from Border Patrol data on enforcement outcomes, a second major source of information
about unauthorized migration and border security is survey data based on interviews with
migrants and potential migrants. Much of the research on unauthorized migration across the
Southwest border focuses on Mexicans because Mexico historically accounts for about 95% of
persons apprehended at the Southwest border.104 An advantage to surveys is that they may collect
more information about their subjects than is found in enforcement data. In addition, because
surveys are conducted within the U.S. interior as well as in migrant countries of origin (i.e.,
Mexico), surveys may capture more information about successful illegal inflows and about the
deterrent effects of enforcement. In 2011, DHS commissioned a comprehensive study by the
National Research Council (NRC) on the use of surveys and related methodologies to estimate
the number of illegal U.S.-Mexico border crossings; and the NRC recommended that DHS use
survey data along with enforcement data to measure illegal flows and the effectiveness of border
enforcement.105
Two binational (U.S.-Mexican) surveys may be particularly useful for estimating illegal flows
because they have examined migration dynamics in migrant-sending and –receiving communities
for a number of years. The surveys are the Mexican Migration Field Research Program
(MMFRP) based at the University of California-San Diego (UCSD) and the Mexican Migration
Project (MMP) based at Princeton University. These targeted surveys ask a number of questions
about U.S. immigration enforcement and how it affects respondents’ migration histories and
future plans. While analysts must account for the likelihood that unauthorized migrants may be
less than forthcoming with interviewers and may be under-represented in certain survey samples,
102 For a fuller discussion, see U.S. Government Accountability Office (GAO), Border Patrol: Key Elements of
Strategic Plan not Yet in Place to Inform Border Security Status and Resource Needs, GAO-13-25, December 2012
(hereafter: GAO, Key Elements of Strategic Plan.) Also see Elliot Spagat, “Under Pressure, Border Patrol Now Counts
Getaways,” Associate Press, April 22, 2013.
103 Ibid., p. 30.
104 Mexicans accounted for about 59% of unauthorized migrants in the United States in 2011; see Michael Hoefer,
Nancy Rytina, and Bryan Baker, Estimates of the Unauthorized Immigrant Population Residing in the United States:
January 2011, Department of Homeland Security, Office of Immigration Statistics, Washington, DC, March 2011. For
a fuller discussion, see CRS Report R42560, Mexican Migration to the United States: Policy and Trends, coordinated
by Ruth Ellen Wasem.
105 NRC, Options for Estimating Illegal Entries, pp. 5-4 – 5-15.
Congressional Research Service
24
Border Security: Immigration Enforcement Between Ports of Entry
a body of social science research has made use of these data and developed commonly cited
methodologies to account for these and other challenges.106
Probability of Apprehension
The UCSD and Princeton surveys both include data, based on self-reporting by people who have
previously attempted to migrate illegally, on the probability that an alien will be apprehended on
any given attempted crossing. According to the Princeton data, the probability of being
apprehended on any given crossing averaged about .37 in the two decades before IRCA’s passage,
ranging from a low of .31 to a high of .42 during this period. The probability of apprehension was
somewhat lower in the decade after IRCA’s passage, ranging from .22 to .32 between 1986 and
1995, and averaging .26 for the decade. Between 1996 and 2010, the last year for which sufficient
data are available, the apprehension rate returned to an average of .36, with a low of .29 and a
high of .50 during these years.107
The UCSD data suggest slightly higher apprehension rates, and show broadly similar trends.
According to these data, the probability of being apprehended on any given crossing averaged .51
between 1974 and 1983, ranging from .32 to .67 during this period. After peaking at .67 in 1981,
the probability of apprehension fell steadily to a low of .34 in 1992-1993. Since 1994 the
probability of apprehension has averaged .49, ranging from .30 to .58 during this period.108 The
UCSD and the Princeton estimates of apprehension rates are substantially lower than the Border
Patrol’s current estimate, which is between .67 and .86.109
Border Deterrence
The Princeton and UCSD surveys thus find that unauthorized migrants are apprehended about a
third to one-half of the time on any given crossing attempt. Both surveys also find that most
aliens who attempt to cross illegally eventually succeed, meaning border deterrence rates are low.
According to the Princeton data, between 75% and 90% of aliens apprehended at the border
between 1965 and 2009 made a subsequent attempt to re-enter the United States and between
55% and 88% eventually succeeded. Border deterrence (i.e., the proportion of aliens who failed to
re-enter the United States) averaged 37% in the two decades before IRCA’s passage; averaged
26% between 1986 and 1995, reaching an all-time low of 21% in 1989; and averaged 34% in
1996-2009, the last year for which sufficient data are available. The UCSD survey finds at-the-
border deterrence rates below 10% for the entire post-1980 period.110
106 See for example, Wayne A. Cornelius and Idean Salehyan, “Does border enforcement deter unauthorized
immigration? The case of Mexican migration to the United States of America,” Regulation & Governance 1.2 (2007):
pp. 139-153; Manuela Angelucci, “U.S. Border Enforcement and the Net Flow of Mexican Illegal Migration,”
Economic Development and Cultural Change, 60, 2 (2012):311-357.
107 CRS Calculations based on data provided by Princeton University Mexico Migration Project. All figures are based
on three-year moving averages of annual apprehension probabilities.
108 CRS calculations based on data provided by University of California-San Diego Mexico Migration Field Research
Project. All figures are based on three-year moving averages of annual apprehension probabilities. Figures are based on
total apprehensions divide by total trips, not once-or-more apprehension rates by individual migrants.
109 Estimates provided by CBP Office of Congressional Affairs, April 24, 2013. Border Patrol reportedly estimates
apprehensions using a methodology broadly similar to the capture-recapture method discussed elsewhere in this report
(see “Estimating Illegal Flows Using Recidivism Data”).
110 Survey data on at-the-border deterrence may under-estimate deterrence rates due to the difficulty of measuring
(continued...)
Congressional Research Service
25
Border Security: Immigration Enforcement Between Ports of Entry
Smuggling Fees
Princeton and UCSD surveys indicate that the majority of unauthorized migrants to the United
States make use of human smugglers (often referred to in Mexico as “coyotes” or “polleros”) to
facilitate their illegal admission to the country. Indeed, whereas about 80% of unauthorized
migrants from Mexico reportedly relied on human smugglers during the 1980s, about 90% did so
in 2005-2007, though the use of smugglers may have declined a bit during the recent economic
downturn.111 Migrants’ reliance on human smugglers, along with prices charged by smugglers, are
an additional potential indicator of the effectiveness of U.S. border enforcement efforts, as more
effective enforcement should increase the costs to smugglers of bringing migrants across the
border, with smugglers passing such costs along to their clients in the form of higher fees.112
Figure 8 summarizes data from the Princeton and UCSD surveys describing average smuggling
fees paid by certain unauthorized migrants from Mexico to the United States. In both cases, the
data reflect reported smuggling fees based on surveys conducted with unauthorized migrants in
the United States and in Mexico (i.e., after migrants had returned home), with fees adjusted for
inflation and reported in 2010 dollars.
(...continued)
successful entry on a single trip, versus successful entry over the course of a lifetime.
111 See Princeton University Mexican Migration Project, “Access to Border-Crossing Guides and Family/Friends on
First Undocumented Trip,” http://mmp.opr.princeton.edu/results/002coyote-en.aspx.
112 See Bryan Roberts, Gordon Hanson, and Derekh Cornwell et al., An Analysis of Migrant Smugglng Costs along the
Southwest Border, DHS Office of Immigration Statistics, Washington, DC, November 2010. The extent to which
smugglers may pass their costs along to migrants also depends on the elasticity of migration with respect to such costs,
as Roberts et al. discuss; smuggling fees may also therefore depend on the broader migration context, including
economic “pulls” and “pushes” in the United States and its migration partner states.
Congressional Research Service
26
Border Security: Immigration Enforcement Between Ports of Entry
Figure 8. Smuggling Fees Paid by Unauthorized Mexican Migrants, 1980-2010
Source: Princeton University Mexican Migration Project (MMP) and University of California, San Diego Mexican
Migration Field Research Program (MMFRP).
Notes: Data based on surveys of unauthorized Mexican migrants about their most recent unauthorized trip to
the United States, with reported amounts adjusted for inflation using Bureau of Labor Statistics Consumer Price
Index Research Series Using Current Methods (CPI-R-US). Data are a weighted three-year average to account
for a small sample size. MMFRP estimate for 2010 may be unreliable due to a small sample size for that year.
According to these data, smuggling fees were mostly flat between 1980 and 1993, at about $600-
$850, with an average annual real growth rate of 1.5%-02.0%. Smuggling fees in both samples
began to rise beginning around 1994, and climbed by an average of 11% per year between 1994
and 2002, reaching about $2,000 in both samples by 2002. Growth in smuggling fees has been
slower since then, averaging 3.7% per year in the Princeton sample and 1.8% in the UCSD
sample (excluding data from 2010, a year in which a small sample may have resulted in an
unreliable annual estimate).113 Thus, these data suggest that crossing the border illegally became
somewhat more difficult—or at least most expensive—in the decade after the USBP began to
implement its 1994 national strategy.
Metrics of Border Security
Some Members of Congress and others have asked the Border Patrol to provide a clear measure
of how many aliens cross the border illegally and/or of the overall state of border security,114 but
measuring illegal border flows is difficult for the obvious reason that unauthorized aliens seek to
113 All data are CRS calculations based on data provided by Princeton University Mexico Migration Project and UCSD
Mexican Migration Field Research Project.
114 See for example, U.S. Congress, House Committee on Homeland Security, Subcommittee on Borders and Maritime
Security, Measuring Outcomes to Understand the State of Border Security, 113th Congress, 1st sess., March 20, 2013;
U.S. Congress, Senate Committee on Homeland Security and Governmental Affairs, Border Security: Measuring
Progress and Addressing the Challenges, 113th Congress, 1st sess., March 14, 2013.
Congressional Research Service
27
Border Security: Immigration Enforcement Between Ports of Entry
avoid detection. While the Border Patrol has accurate data on various enforcement outcomes,
these enforcement data were not designed to measure overall illegal inflows. Thus, DHS officials
have testified that current enforcement data do not offer a suitable metric to describe border
security.115
Apprehensions data are imperfect indicators of illegal flows because they exclude two important
groups when it comes to unauthorized migration: aliens who successfully enter and remain in the
United States (i.e., enforcement failures) and aliens who are deterred from entering the United
States (i.e., certain enforcement successes). Thus, analysts do not know if a decline in
apprehensions is an indicator of successful enforcement, because fewer people are attempting to
enter, or of enforcement failures, because more of them are succeeding.116 A further limitation to
apprehensions data is that they count events, not unique individuals, so the same person may
appear multiple times in the dataset after multiple entry attempts.
Unique apprehensions and USBP’s estimate of got aways and turn backs are designed, in part, to
address these limitations, but they offer only partial solutions. Unique apprehensions address the
“overcount” problem associated with recidivism, but still misses information about certain
enforcement failures (got-aways) and certain enforcement successes (deterrence). Estimated got
aways and turn backs attempt to grapple with the latter problem; but (like apprehensions) they
count events rather than individuals. Moreover, because estimated got-aways and turn backs
attempt to measure enforcement outcomes that do not result in apprehensions, they are heavily
dependent on the subjective judgment of individual border agents.117 To the extent that agents—or
the agency—are rewarded for effective enforcement, some people may question the credibility of
a measure based on such judgments. Indeed, some media reports already have raised questions
about the accuracy of the got away and turn back data.118 The Border Patrol issued new guidance
in September 2012 designed to impose greater consistency on turn back and got away data
collection and reporting,119 but data from the new system have not yet been analyzed.
A further limitation of enforcement data is that all such data depend on enforcement resources. In
general, USBP enforcement outcomes (e.g., apprehensions, estimated got aways) are a function of
(1) the underlying illegal flows and (2) the agency’s ability to detect such flows. Enforcement
data alone cannot disentangle these two factors. As a result, enforcement data may tend to
overestimate illegal flows where resources are robust, and to under-estimate such flows where
resources are scarce.
115 U.S. Congress, House Committee on Homeland Security, Subcommittee on Borders and Maritime Security,
Measuring Outcomes to Understand the State of Border Security, testimony of Assistant Commissioner of Homeland
Security Mark Borkowski, 113th Congress, 1st sess., March 20, 2013; U.S. Congress, House Committee on Homeland
Security, Subcommittee on Borders and Maritime Security, Measuring Outcomes to Understand the State of Border
Security, testimony of Border Patrol Chief Michael Fisher, 113th Congress, 1st sess., March 20, 2013. Also see U.S.
Congress, House Committee on Homeland Security, Subcommittee on Border and Maritime Security, What Does a
Secure Border Look Like, testimony by Marc R. Rosenblum, 113th Cong., 1st sess., February 26, 2013.
116 See Edward Alden and Bryan Roberts, “Are U.S. Borders Secure? Why We Don’t Know and How to Find Out,”
Foreign Affairs 90, 4 (2011): pp. 19-26.
117 For a fuller discussion, see GAO, Key Elements of Strategic Plan, pp. 28-31.
118 See for example, Andrew Becker, “New Drone Radar Reveals Border Patrol ‘Gotaways’ in High Numbers,” Center
for Investigative Reporting, April 4, 2013.
119 GAO, Key Elements of Strategic Plan, p. 24.
Congressional Research Service
28
Border Security: Immigration Enforcement Between Ports of Entry
Given the limits of existing border enforcement data, DHS and outside researchers have
developed several different metrics for estimating illegal border flows and describing border
security. Three different methods for estimating illegal migration stocks and flows are described
in the remainder of this section, and broad conclusions based on these metrics are described
below (see “How Secure is the U.S. Border?”).120
The Residual Method for Estimating Unauthorized Residents in
the United States
Arguably the most well-developed approach to measuring unauthorized migration focuses on the
number of unauthorized migrants residing in the United States. For many years, analysts within
DHS and other social scientists have used the so-called “residual method” to estimate this
number. In essence, the method involves using legal admissions data to estimate the legal,
foreign-born population, and then subtracting this number from the overall count of foreign-born
residents based on U.S. census data.121
The residual method provides limited information about the border per se because many
unauthorized residents enter the United States through ports of entry, lawfully or otherwise.122
Nonetheless, estimates of the size of the unauthorized population may offer several advantages
over the border metrics discussed below. First, for many people, how many unauthorized aliens
reside within the United States ultimately is a more important question than how many cross the
border. After all, if illegal border flows fall to zero, but many people continue to enter illegally
through ports of entry or by overstaying nonimmigrant visas, many people would consider such
an outcome problematic. Second, for this reason, the size of the unauthorized population more
comprehensively reflects how well immigration policy and immigration enforcement function,
including for example the effectiveness of worksite and other interior enforcement efforts as well
as how well visas meet employer and family demands. Third, estimates of the unauthorized
population offer the advantage of a nearly 30-year track record and a relatively uncontroversial
methodology. As long ago as 2001, the Department of Justice used the total estimated stock of
unauthorized migrants in the United States as a key performance metric for the department’s
evaluation of its border security efforts.123
120 For a fuller discussion of border metric methodologies and additional estimates of border security, also see Bryan
Roberts, John Whitley and Edward Alden, Managing lllegal Immigration to the United States: How Effective is
Enforcement? New York: Council on Foreign Relations Press, 2013 (hereafter: Roberts et al., Managing Illegal
Immigration to the United States).
121 For a clear discussion of this methodology, see Jeffrey S. Passel, “The Size and Characteristics of the Unauthorized
Migrant Population in the U.S.,” Pew Hispanic Center, March 6, 2006, http://www.pewhispanic.org/2006/03/07/size-
and-characteristics-of-the-unauthorized-migrant-population-in-the-us/. Also see CRS Report RL33874, Unauthorized
Aliens Residing in the United States: Estimates Since 1986, by Ruth Ellen Wasem.
122 In general, unauthorized migrants enter the United States three ways: by crossing the border without inspection
between ports of entry (the focus of this report); by entering illegally through ports of entry, either by using a
fraudulent document or by hiding in a vehicle; or by entering legally and then overstaying a temporary visa or
becoming deportable for some other reason.
123 See Department of Justice, FY2001 Performance Report & FY2002 Revised Final, FY2003 Performance Plan,
Washington, DC 2001, pp. 120-122.
Congressional Research Service
29
Border Security: Immigration Enforcement Between Ports of Entry
CBP Metrics of Border Security
Operational Control of the Border
Section 2 of the Secure Fence Act of 2006 (P.L. 109-367) defines operational control of the
border to mean “the prevention of all unlawful entries into the United States, including entries by
terrorists, other unlawful aliens, instruments of terrorism, narcotics, and other contraband.” Most
experts agree that preventing 100% of unlawful entries across U.S. borders is an impossible
task;124 and through FY2010, the Border Patrol classified portions of the border as being under
“effective” or “operational” control if the agency “has the ability to detect, respond, and interdict
illegal activity at the border or after entry into the United States.”125 The agency conducted a five-
level assessment of border security, with the two top levels (“controlled” and “managed”) defined
as being under effective control, and the three remaining levels (“monitored,” “low-level
monitored,” and “remote/low activity”) defined as not being under effective control.126 In
February 2010, the Border Patrol reported that 1,107 miles (57%) of the Southwest border were
under effective control.127
Beginning in FY2011, USBP stopped using this measure of effective control.128 The agency
reportedly no longer views operational or effective control as a useful metric because station and
sector chiefs could not accurately and reliably use the five-level coding scheme to assess different
border regions.129 In addition, given the dynamic nature of border threats, the agency does not
view it as useful to evaluate border security on a mile-by-mile basis.130
Border Conditions Index
In May 2011, DHS announced that CBP was developing a new “border conditions index”
(BCI).131 Reportedly, the BCI will include measures of estimated illegal flows between ports of
entry, wait times and the efficiency of legal flows at ports of entry, and public safety and quality
of life in border regions. These three components will be combined to develop a holistic “score”
calculated for different regions of the border.132 With these different components, the BCI
124 See, for example, Edward Alden and Bryan Roberts, “Are US Borders Secure? Why We Don't Know, and How to
Find Out,” Foreign Affairs, vol. 90, no. 4 (July/August 2011), pp. 19-26.
125 U.S. Government Accountability Office, Border Security: Preliminary Observations on Border Control Measuers
for the Southwest Border, GAO-11-374T, February 15, 2011, p. 7.
126 Ibid., p. 8.
127 U.S. Congress, House Committee on Homeland Security, Subcommittee on Border and Maritime Security, Securing
Our Borders: Operational Control and the Path Forward, 112th Congress, 1st sess., February 15, 2010.
128 DHS did not report on border miles under effective control in its FY2010 Annual Performance Report; see DHS,
Annual Performance Report: Fiscal Years 2010-2012, Washington, DC, April 2011, http://www.dhs.gov/xlibrary/
assets/cfo_apr_fy2010.pdf.
129 CBP Office of Congressional Affairs, March 15, 2013.
130 U.S. Congress, House Committee on Homeland Security, Subcommittee on Borders and Maritime Security,
Measuring Outcomes to Understand the State of Border Security, testimony of Border Patrol Chief Michael Fisher,
113th Congress, 1st sess., March 20, 2013.
131 U.S. Congress, Senate Committee on Homeland Security and Governmental Affairs, Securing the Border: Progress
at the Federal Level, testimony of Secretary of Homeland Security Janet Napolitano, 112th Cong., 1st sess., May 4,
2011.
132 CBP Office of Congressional Affairs, December 9, 2011.
Congressional Research Service
30
Border Security: Immigration Enforcement Between Ports of Entry
includes some of the same information some Members of Congress and others may consider to be
of interest with respect to describing border security; but DHS officials have emphasized that the
BCI encompasses a broader set of issues than “border security” as this term is normally used, and
that the BCI therefore may not satisfy demands for a single comprehensive measure of border
security.133 Officials have also testified that the BCI remains in the development phase.134
Border Patrol Effectiveness Rate
By dividing apprehensions and estimated turn backs (i.e., successful enforcement outcomes) by
estimated known illegal entries (see “Estimated “Got Aways” and “Turn Backs””), USBP
calculates an estimated enforcement effectiveness rate. Some people have proposed using this
effectiveness rate as a measure of border security. While using enforcement data to measure
border security raises a number of methodological concerns (see “Metrics of Border Security”),
the effectiveness rate would have an advantage over other enforcement metrics because, as a
ratio, it may be somewhat less sensitive to the level of enforcement resources in place.135 As with
the BCI, it is difficult to evaluate USBP’s effectiveness rate as a border metric because little is
known about the agency’s new protocols for collecting got away and turn back data.
Estimating Illegal Flows Using Recidivism Data
For many years, social scientists have used the so-called “capture-recapture” method to estimate
unauthorized flows based on recidivism data.136 The capture-recapture method estimates the total
flow of unauthorized migrants based on the ratio of persons re-apprehended after an initial
enforcement action to the total number of persons apprehended.137 In the basic model, the
probability of apprehension is calculated by taking the ratio of recidivist apprehensions to total
apprehensions; and the total illegal inflow is calculated by dividing total apprehensions by the
odds of apprehension.138 See Appendix for more details.
An advantage to the capture-recapture method is that it relies on observable administrative
enforcement data—apprehensions and recidivists—to calculate key border security metrics:
apprehension rates and illegal flows. Yet the basic model assumes that all intending unauthorized
133 U.S. Congress, House Committee on Homeland Security, Subcommittee on Borders and Maritime Security,
Measuring Outcomes to Understand the State of Border Security, testimony of Assistant Commissioner of Homeland
Security Mark Borkowski, 113th Congress, 1st sess., March 20, 2013.
134 Ibid.
135 That is, whereas using apprehensions as a metric of border security is problematic because apprehensions depend on
border resources, the ratio of apprehensions to got aways is somewhat less problematic because both apprehensions and
estimated known got aways depend on resources, so the ratio may more accurately reflect the proportion of aliens that
successfully enters. Nonetheless, the ratio may still be sensitive to border resources if estimating inflows is less (or
more) resource-intensive than apprehending aliens. And the enforcement rate by itself may not be an acceptable metric
without also considering data on total illegal attempts: many would consider a 10% effectiveness rate based on 100
entry attempts to be more effective than a 90% rate based on a million attempts, for example.
136 According to CBP Office of Congressional Affairs December 20, 2011 and more recent CRS conversations with
DHS officials, DHS reportedly plans to use a capture-recapture model as one element of the border conditions index
(BCI).
137 Thomas J. Espenshade, “Using INS Border Apprehension Data to Measure the Flow of Undocumented Migrants
Crossing the U.S.-Mexico Frontier,” International Migration Review, vol. 29, no. 2 (Summer 1995), pp. 545-565.
138 In statistical methods, the odds of apprehension equal the probability of apprehension divided by one minus the
probability of apprehension; see Ibid.
Congressional Research Service
31
Border Security: Immigration Enforcement Between Ports of Entry
migrants eventually succeed (i.e., that none are deterred at the border).139 To the extent that the
build-up in border enforcement resources and the deployment of the Consequence Delivery
System cause some would-be unauthorized migrants to give up and return home, the capture-
recapture method underestimates successful enforcement and overestimates illegal flows.
Likewise, the basic model assumes that all border crossers originate in—and are repatriated to—
Mexico, facilitating re-entry attempts. As the proportion of border crossers from countries other
than Mexico increases—as it has in recent years—140repatriated aliens may be less likely to
attempt re-entry, an additional reason the capture-recapture model may over-estimate illegal
inflows.
Thus, to estimate illegal flows based on the capture-recapture method, enforcement data on
apprehensions and repeat apprehensions must be supplemented with additional information about
the proportion of migrants deterred, and must control for lower recidivism rates among non-
Mexicans.141 Estimates of illegal flows based on this methodology are discussed below (see
“How Secure is the U.S. Border?”).
How Secure is the U.S. Border?
While no single metric accurately and reliably describes border security (see “Metrics of Border
Security”), most analysts agree, based on available data, that the number of illegal border crossers
fell sharply between about 2005 and 2011, with some rise in illegal flows in 2012. This
conclusion is supported by key Border Patrol enforcement data described above, including the
drop in total apprehensions, the drop in unique apprehensions, and the drop in estimated got
aways and total estimated known entries across eight out of nine Border Patrol sectors.
Survey data confirm an apparent drop in illegal inflows, and measure such effects away from the
border. For example, according to data collected by the Princeton Mexican Migration Project, an
average of about 2% of all Mexican men initiated a first unauthorized trip to the United States
each year between 1973 and 2002; but that percentage has fallen sharply since 2002, to below
0.4% in 2008-2011.142 Estimates of the unauthorized population based on the residual method
report drops of about 1 million unauthorized migrants living in the United States, from about 12.4
million in 2007 to 13.1 million in 2011.143 And the Pew Hispanic Center estimates that net (i.e.,
139 Ibid. The basic model also assumes that that the odds of being apprehended are the same across different border
regions and across multiple attempts to cross the border.
140 Mexicans accounted for 87% of USBP apprehensions in FY2010, 84% in FY2011, and 73% in FY2012, the three
lowest proportions ever recorded.
141 See Roberts et al., Managing lllegal Immigration to the United States); Panel on Survey Options for Estimating the
Flow of Unauthorized Crossings at the U.S.-Mexico Border, Options for Estimating Illegal Entries at the U.S.-Mexico
Border, Washington, DC: National Research Council, 2012 (hereafter: NRC, Options for Estimating Illegal Entries).
Accounting for deterrence, flows are estimated to be equal to the number of total apprehensions divided by the the odds
of successful enforcement; and the probability of successful enforcement is defined as the number of recidivists divided
by total apprehensions, divided by one minus the probability of deterrence.
142 Princeton University Mexican Migration Project, “Probability of a Mexican Taking a First U.S. Trip,”
http://mmp.opr.princeton.edu/results/009firsttrip-en.aspx.
143 Jeffrey Passel and D’Vera Cohn, “Unauthorized Immigrants: 11.1 Million in 2011,” Pew Hispanic Center,
December 6, 2012, http://www.pewhispanic.org/2012/12/06/unauthorized-immigrants-11-1-million-in-2011/; also see
CRS Report R42988, U.S. Immigration Policy: Chart Book of Key Trends, by William A. Kandel.
Congressional Research Service
32
Border Security: Immigration Enforcement Between Ports of Entry
northbound minus southbound) unauthorized migration from Mexico fell to about zero in 2011,
and that outflows may have even exceeded inflows.144
According to GAO’s analysis of Border Patrol metrics, eight out of nine Border Patrol sectors (all
except the Big Bend sector) showed improved effectiveness rates between FY2006 and
FY2011.145 In the Tucson sector, the main focus of GAO’s analysis, the effectiveness rate
improved from 67% to 87% during this period. The San Diego, El Centro, Yuma, and El Paso
sectors all had effectiveness rates in FY2011 of about 90%; the Del Rio and Laredo sectors (along
with Tucson) had rates above 80%; and the Big Bend and Rio Grande Valley sectors had rates
between 60% and 70%.
CRS estimates based on USBP recidivism data and using the capture-recapture method also
suggest that illegal flows between ports of entry fell substantially between 2005 and 2011, before
rising somewhat in 2012 (see Figure 9). The shaded area in Figure 9 depicts total estimated
illegal inflows, which are equal to the total number of apprehensions divided by the estimated
odds of successful enforcement. (See Appendix for a discussion of the methodology used to
generate Figure 9.) Based on available data, the figure assumes deterrence rates in 2000-2012
were between 20% (the estimates depicted by the upper bound of the shaded area) and 40% (the
lower bound). As the figure indicates, total estimated illegal inflows fell from a high of between
760,000 and 1.4 million in 2004 to a low of between 340,000 and 580,000 in 2009-2010.146 The
model estimates that total illegal inflows were between 400,000 and 660,000 in 2012. Although
recidivism data are not available to make similar calculations for previous years, apprehension
levels and survey data from the 1980s and 1990s suggest that total illegal inflows likely were
lower in 2007-2012 than at any other point in the last three decades.
144 Jeffrey Passel, D’Vera Cohn and Ana Gonzalez-Barrera, “Net Migration from Mexico Falls to Zero—and Perhaps
Less,” Washington, DC: Pew Hispanic Center, May 3, 2012.
145 GAO, Key Elements of Strategic Plan, pp. 74-82. Effectiveness rates in this paragraph are defined as the proportion
of known illegal entrants who are apprehended or return to Mexico; effectiveness rates are lower if turn-backs are not
counted in the numerator.
146 As Figure 9 illustrates, the model estimates that illegal inflows reached their lowest point in 2009 if deterrence is
assumed to be 40%, while inflows reached their lowest point in 2011 if deterrence is assumed to be 20%.
Congressional Research Service
33
Border Security: Immigration Enforcement Between Ports of Entry
Figure 9. Total Estimated Illegal Border Inflows, by Assumed Rate of Deterrence
FY2000-FY2012
Source: CRS Analysis based on data provided by CBP Office of Congressional Affairs.
Notes: See text for discussion of methodology.
Border enforcement is only one of several factors that affect illegal migration.147 Thus, if illegal
entries indeed fell after 2006, to what degree is this change attributable to enforcement versus
other developments, such as the U.S. economic downturn since 2007, and/or economic and
demographic changes in Mexico and other countries of origin?148 Disentangling the effects of
enforcement from other factors influencing migration flows is particularly difficult in the current
case because many of the most significant new enforcement efforts—including a sizeable share of
new border enforcement personnel, most border fencing, new enforcement practices at the border,
and many of the new migration enforcement measures within the United States—all have
occurred at the same time as the most severe recession since the 1930s.
Nonetheless, the drop in recidivism rates suggests that an increasing proportion of aliens are
being deterred by CBP’s enforcement efforts, a finding that also appears to be reflected in survey
data from the Princeton survey (see “Border Deterrence”). Surveys of unauthorized migrants
repatriated to Mexico in 2005 and 2010 also suggest that enforcement is increasingly likely to
deter future immigration.149 As Figure 9 illustrates, the more unauthorized migrants that are being
deterred by U.S. enforcement efforts, the lower the number of successful illegal inflows.
147 See, for example, Douglas S. Massey, Joaquin Arango, and Graeme Hugo et al., Worlds In Motion: Understanding
International Migration at the End of the Millenium, 2nd ed. (New York: Oxford University Press, 2005).
148 On the effects of Mexico’s falling birthrate on U.S. immigration, see Gordon H. Hanson, Esther Duflo, and Craig
McIntosh, “The Demography of Mexican Migration to the United States,” American Economic Review, vol. 99, no. 2
(May 2009), pp. 22-27. Also see CRS Report R42560, Mexican Migration to the United States: Policy and Trends,
coordinated by Ruth Ellen Wasem.
149 Among Mexicans who migrated illegally to look for work (83% of those in the survey), 60% of those repatriated in
2010 reported that they intended to return to the United States immediately, and 80% reported that they intended to
(continued...)
Congressional Research Service
34
Border Security: Immigration Enforcement Between Ports of Entry
Academic research from 2012 also provides evidence that border enforcement has contributed to
a reduction in illegal flows.150 These findings are noteworthy, in part, because they contradict
earlier academic research, much of which found that border enforcement had a limited impact or
even was counter-productive when it came to migration control efforts (also see “Migration
Flows: “Caging” Effects and Alternative Modes of Entry”).151 This research suggests that the
recent build-up in immigration enforcement at the border and within the United States may have
had a greater deterrent effect on illegal migration than earlier efforts.152 Nonetheless, some
uncertainty will remain about the true level of border security as long as U.S. employment
demand remains below historic levels.
Unintended and Secondary Consequences of
Border Enforcement
The preceding discussion includes estimates of what may be described as the primary costs and
benefits of border enforcement, defined in terms of congressional appropriations and deployment
of enforcement resources on one hand, and alien apprehensions and other indicators of successful
enforcement on the other. A comprehensive analysis of the costs and benefits of border
enforcement policies may also consider possible unintended and secondary consequences. Such
consequences may produce both costs and benefits—many of which are difficult to measure—in
at least five areas: border-area crime and migrant deaths, migrant flows, environmental impacts,
effects on border communities, and U.S. foreign relations.
Border-Area Crime and Migrant Deaths
Illegal border crossing is associated with a certain level of border crime and violence and, in the
most unfortunate cases, with deaths of illegal border crossers and border-area law enforcement
officers. Unauthorized migration may be associated with crime and mortality in several distinct
ways. First, unauthorized migration is associated with crime—apart from the crime of illegal
entry—because some unauthorized migrants contract with immigrant smugglers and because
(...continued)
return eventually, down from 81% and 92%, respectively, in 2005. Among new unauthorized migrants (those who had
spent less than a week in the United States before being repatriated to Mexico), 18% of those repatriated in 2010
reported that they would not return to the United States compared to 6% in 2005. See Jeffrey Passel, D'Vera Cohn, and
Ana Gonzalez-Barrera, Net Migration from Mexico Falls to Zero—And Perhaps Less, Pew Hispanic Center,
Washington, DC, 2012, http://www.pewhispanic.org/files/2012/04/PHC-04-23a-Mexican-Migration.pdf, pp. 24-25.
150 See for example, Scott Borger, Gordon Hanson, and Bryan Roberts “The Decision to Emigrate From Mexico,”
presentation at the Society of Government Economists annual conference, November 6, 2012; Manuela Angelucci,
“U.S. Border Enforcement and the Net Flow of Mexican Illegal Migration,” Economic Development and Cultural
Change, 60, 2 (2012):311-357; Rebecca Lessem. “Mexico-US Immigration: Effects of Wages and Border
Enforcement,” Carnegie Mellon University, Research Showcase, May 2, 2012.
151 See for example, Wayne Cornelius, “Evaluating Recent US Immigration Control Policy: What Mexican Migrants
Can Tell Us,” in Crossing and Controlling Borders: Immigration Policies and Their Impact on Migrants’ Journeys, ed.
Mechthild Baumann, Astrid Lorenz, and Kerstin Rosenhow (Farmington, MI: Budrich Unipress Ltd, 2011); Douglas S.
Massey, Jorge Durand, and Nolan J. Malone, Beyond Smoke and Mirrors: Mexican Immigration in an Era of Economic
Integration (Russell Sage Foundation, 2002).
152 See Manuela Angelucci, “U.S. Border Enforcement and the Net Flow of Mexican Illegal Migration,” Economic
Development and Cultural Change, 60, 2 (2012):311-357.
Congressional Research Service
35
Border Security: Immigration Enforcement Between Ports of Entry
unauthorized migrants may engage in related illegal activity, such as document fraud. Yet fear of
the police may make unauthorized aliens less likely to engage in other types of criminal activity,
and research on the subject finds low immigrant criminality rates, especially when accounting for
education levels and other demographic characteristics.153 Second, illegal border crossers face
risks associated with crossing the border at dangerous locations, where they may die from
exposure or from drowning.154
Border enforcement therefore may affect crime and migrant mortality in complex ways.155 On one
hand, the concentration of enforcement resources around the border may exacerbate adverse
outcomes by making migrants more likely to rely on smugglers, as noted above (see “Smuggling
Fees”). The 1994 National Strategic Plan predicted a short-term rise in border violence for these
reasons.156 On the other hand, to the extent that enforcement successfully deters illegal crossers,
such prevention should reduce crime and mortality. The concentration of law enforcement
personnel near the border may further enhance public safety and migrant protection, especially
where CBP has made a priority of protecting vulnerable populations.157
The empirical record suggests that there is no significant difference in the average violent crime
rate in border and non-border metropolitan areas.158 Indeed, the border cities El Paso, TX, and
San Diego, CA, are regularly listed among the safest large cities in the country based on their
rankings among similarly sized cities in the Federal Bureau of Investigation’s Uniform Crime
Report.159 The specific impact of border enforcement on border-area crime is unknown, however,
because available data cannot separate the influence of border enforcement from other factors.160
153 See CRS Report R42057, Interior Immigration Enforcement: Programs Targeting Criminal Aliens, by Marc R.
Rosenblum and William A. Kandel.
154 In 2011, for example, of the 238 migrants deaths for which DHS was able to determine a cause of death, 139 were
attributed to exposure to heat or cold or water-related; data provided to CRS by CBP Office of Congressional Affairs
December 15, 2011.
155 Also see Karl Eschbach, Jacqueline Hagan, and Nestor Rodriguez et al., “Death at the Border,” International
Migration Review, vol. 33, no. 2 (Summer 1999), pp. 430-454.
156 National Strategic Plan, p. 11-12.
157 The USBP’s Border Patrol Search, Trauma, and Rescue Unit (BORSTAR) is comprised of agents with specialized
skills and training for tactical medical search and rescue operations. BORSTAR agents provide rapid response to search
and rescue and medical operations, including rescuing migrants in distress.
158 For a fuller discussion, see CRS Report R41075, Southwest Border Violence: Issues in Identifying and Measuring
Spillover Violence, by Kristin Finklea.
159 See for example, Daniel Borunda, “El Paso Ranked Safest Large city in U.S. for 3rd Straight Year,” El Paso Times,
February 6, 2013, http://www.elpasotimes.com/ci_22523903/el-paso-ranked-safest-large-city-u-s.
160 Uniform Crime Report (UCR) data provide the most information about crime rates, but they are not sufficiently
fine-tuned to provide information on the diverse factors affecting such trends; see CRS Report RL34309, How Crime in
the United States Is Measured, by Nathan James and Logan Rishard Council.
Congressional Research Service
36
Border Security: Immigration Enforcement Between Ports of Entry
Figure 10. Known Migrant Deaths, Southwest Border, 1985-2012
Source: University of Houston Center for Immigration Research (CIR); Jimenez, “Humanitarian Crisis,” 2009
(ACLU); CBP Office of Congressional Affairs March 13, 2013 (DHS).
With respect to mortality, available data about migrant deaths along the Southwest border are
presented in Figure 10.161 The figures come from academic research based on local medical
investigators’ and examiners’ offices in California, Arizona, New Mexico, and Texas between
1985 and 1998 (the University of Houston’s Center for Immigration Research, CIR); Mexican
foreign ministry and Mexican media counts compiled by the American Civil Liberties Union of
San Diego; and data compiled by DHS based on bodies recovered on the U.S. side of the
border.162 All three data sources reflect known migrant deaths, and therefore undercount actual
migrant deaths since some bodies may not be discovered.163 Additionally, U.S. data sources
generally do not include information from the Mexican side of the border and therefore further
undercount migration-related fatalities.
As Figure 10 illustrates, data from the CIR indicate that known migrant deaths fell from a high of
344 in 1988 to a low of 171 in 1994 before climbing back to 286 in 1998. According to DHS data,
known migrant deaths climbed from 250 in 1999 to 492 in 2005, and averaged 431 deaths per
year in 2005-2009. DHS’s count fell to an average of 369 per year in 2010-2011, but increased to
463 in FY2012. And the ACLU found that known migrant deaths increased from just 80 per year
161 CRS attempted to obtain more current data (i.e., FY2013 and FY2014), however, according to DHS, the data are not
available for release. CRS email with DHS Congressional Affairs office on November 13, 2014.
162 See Stanley Bailey, Karl Eschbach, and Jacqueline Hagan et al., “Migrant Death on the US-Mexco Border 1985-
1996,” University of Houston Center for Immigration Research Working Paper Series, vol. 96, no. 1 (1996); Jimenez,
“Humanitarian Crisis,” 2009.
163 The Border Patrol has drawn criticism from human rights activists who claim that the agency’s migrant death count
understates the number of fatalities. Some contend that the Border Patrol undercounts fatalities by excluding skeletal
remains, victims in car accidents, and corpses discovered by other agencies or local law enforcement officers; see , for
example, Raymond Michalowski, “Border Militarization and Migrant Suffering: A Case of Transnational Social
Injury,” Social Justice, Summer 2007.
Congressional Research Service
37
Border Security: Immigration Enforcement Between Ports of Entry
in 1993-1996 to 496 per year in 1997-2007. The apparent increase in migrant deaths is
noteworthy in light of the apparent decline in unauthorized entries during the same period. These
data offer evidence that border crossings have become more hazardous since the “prevention
through deterrence” policy went into effect in the 1990s,164 though (as with crime) the precise
impact of enforcement on migrant deaths is unknown.
Migration Flows: “Caging” Effects and Alternative Modes of Entry
With illegal border crossing becoming more dangerous and more expensive, some unauthorized
aliens appear to have adapted their behavior to avoid crossing the border via traditional pathways.
Most notably, social science research suggests that border enforcement has had the unintended
consequence of encouraging unauthorized aliens to settle permanently in the United States rather
than working temporarily and then returning home, as was more common prior to the mid-
1980s.165 The primary evidence for this so-called “caging” effect is that unauthorized migrants
appear to be staying longer in the United States and raising families here more often rather than
making regular trips to visit families that remain in countries of origin.166 Although other factors
also likely contribute to these changes,167 survey results appear to confirm that border
enforcement has been a factor behind these longer stays.168
A second unintended consequence of enhanced border enforcement between ports of entry may
have been an increase in illegal entries through ports of entry and other means. According to
UCSD Mexico Migration Field Research Program research, unauthorized Mexican migrants from
one community in Mexico interviewed in 2009 used six different methods to enter the United
States illegally, with one in four such aliens passing illegally through a port of entry by using
164 Also see Adam Isacson and Maureen Meyer, “Border Security and Migration: A Report from South Texas,”
Washington Office on Latin America, http://www.wola.org/sites/default/files/downloadable/Mexico/2013/
Border%20Security%20and%20Migration%20South%20Texas.pdf.
165 See Wayne Cornelius, “Evaluating Recent US Immigration Control Policy: What Mexican Migrants Can Tell Us,”
in Crossing and Controlling Borders: Immigration Policies and Their Impact on Migrants’ Journeys, ed. Mechthild
Baumann, Astrid Lorenz, and Kerstin Rosenhow (Farmington, MI: Budrich Unipress Ltd, 2011); Douglas S. Massey,
Jorge Durand, and Nolan J. Malone, Beyond Smoke and Mirrors: Mexican Immigration in an Era of Economic
Integration (Russell Sage Foundation, 2002).
166 Whereas almost half of unauthorized aliens from Mexico who arrived in 1980 remained in the United States for less
than a year, fewer than 20% of unauthorized Mexicans who entered in 2010 returned home within a year; see Mexican
Migration Project, “Probability of Return within 12 Months,” http://mmp.opr.princeton.edu/results/010returnpers-
en.aspx. Also see Jonathan Hicken, Mollie Cohen, and Jorge Narvaez, “Double Jeopardy: How U.S. Enforcement
Policies Shape Tunkaseño Migration,” in Mexican Migration and the U.S. Economic Crisis, ed. Wayne A. Cornelius,
David FitzGerald, Pedro Lewin Fischer, and Leah Muse-Orlinoff (La Jolla, CA: University of California, San Diego
Center for Comparative Immigration Studies, 2010), pp. 56-57. And whereas an estimated 60-90% of unauthorized
migrants during the 1970s were single men, by 2008 men only accounted for an estimated 53% of unauthorized aliens,
with women representing 34% and the remainder children; see Jeffrey S. Passel and D’Vera Cohn, A Portrait of
Unauthorized Immigrants in the United States, Pew Hispanic Center, Washington, DC, April 14, 2009, p. 4,
http://pewhispanic.org/files/reports/107.pdf.
167 For example, changes in U.S. labor markets have resulted in more permanent (non-seasonal) employment
opportunities for unauthorized aliens as well as more employment opportunities for unauthorized women; See CRS
Report R41592, The U.S. Foreign-Born Population: Trends and Selected Characteristics, by William A. Kandel.
168 Half of the Mexico-based family members of unauthorized aliens interviewed by the UC, San Diego MMFRP in
2009 indicated that they had a relative who had remained in the United States longer than they had intended because
they feared they would be unable to reenter the United States if they returned home; see Hicken et al. “Double
Jeopardy,” 57-58.
Congressional Research Service
38
Border Security: Immigration Enforcement Between Ports of Entry
borrowed or fraudulent documents or by hiding in a vehicle.169 Based on three different surveys
conducted between 2008 and 2010, UCSD researchers found that the probability of being
apprehended while passing illegally though a port of entry was about half as high as the
probability of being apprehended while crossing between the ports.170 CBP’s Passenger
Compliance Examination (COMPEX) System reportedly detects very little illegal migration
through ports of entry, however.171 There is also anecdotal evidence that unauthorized aliens have
recently turned to maritime routes as alternative strategies to cross the U.S.-Mexican border.172
Environmental Impact
A third set of potential unintended consequences concern the effect of border enforcement on the
environment. As with the effects of enforcement on border crime and violence, the effects of
enforcement on the environment are complex because they reflect changes in migrant behavior
and the secondary effects of enforcement per se.
On one hand, many illegal border crossers transit through sensitive environmental areas, cutting
vegetation for shelter and fire, potentially causing wildfires, increasing erosion through repeated
use of trails, and discarding trash.173 Thus, to the extent that border enforcement successfully
deters illegal flows, enforcement benefits the environment by reducing these undesirable
outcomes. On the other hand, the construction of fencing, roads, and other tactical infrastructure
may damage border-area ecosystems. These environmental considerations may be especially
important because much of the border runs through remote and environmentally sensitive
areas.174 For this reason, even when accounting for the possible environmental benefits of reduced
illegal border flows, some environmental groups have opposed border infrastructure projects
because they threaten rare and endangered species as well as other wildlife by damaging
ecosystems and restricting the movement of animals, and because surveillance towers and
artificial night lighting have detrimental effects on migrant birds.175
Effects on Border Communities and Civil Rights
Although economists disagree about the overall economic impact of unauthorized migration,
unauthorized migrants may impose a number of costs at the local level, including through their
169 Hicken et al., “Double Jeopardy,” pp. 60-61.
170 Probability of apprehension on an alien’s most recent attempt to illegally pass through a port of entry was 0.36,
compared to 0.73 on the most recent entry attempt between ports of entry; UC San Diego MMFRP data provided to
CRS September 23, 2010.
171 CBP Office of Congressional Affairs March 21, 2013.
172 See for example, Adolfo Flores and Ruben Vives, “New Panga Incident Investigated as Possible Smuggling
Operation,” Los Angeles Times, December 10, 2012; Dave Graham, “By Land or by Sea, Tougher U.S. Border Tests
Illegal Immigrants,” Reuters, March 20, 2013. Border tunnels are mainly used to smuggle narcotics into the United
States, rather than for illegal migration.
173 Department of Homeland Security, Environmental Impact Statement for the Completion of the 14-mile Border
Infrastructure System, San Diego, California (July 2003), pp. 1-11.
174 According to the GAO, about 25% of the northern border and 43% of the Southwest border consist of federal and
tribal lands overseen by the U.S. Forest Service and Department of the Interior; see CRS Report R42346, Federal Land
Ownership: Overview and Data, by Carol Hardy Vincent, Laura A. Hanson, and Marc R. Rosenblum.
175 See for example, University of Texas School of Law, “The Texas-Mexico Border Wall,” http://www.utexas.edu/
law/centers/humanrights/borderwall/.
Congressional Research Service
39
Border Security: Immigration Enforcement Between Ports of Entry
use of schools and other public programs.176 Some are also concerned that illegal migration
undermines the rule of law. For these reasons, successful border enforcement may benefit border
communities by reducing illegal inflows.
Yet some business owners on the Southwest and Northern borders have complained that certain
border enforcement efforts threaten their economic activities, including farming and ranching
activities that are disrupted by the deployment of USBP resources to the border and commercial
activities that suffer from reduced regional economic activity.177 More generally, some people
have complained that the construction of barriers divides communities that have straddled
international land borders for generations.178
Some people have raised additional concerns about the effects of border enforcement on civil
rights. Some residents of Southwest and Northern border communities see enhanced border
enforcement as leading to racial profiling and wrongful detentions.179 On top of this general
concern, some people argue that Operation Streamline raises additional questions about whether
migrants receive adequate legal protections during fast-tracked criminal procedures.180 And some
have argued that mistreatment and abuse are widespread in CBP detention facilities.181
An additional concern that some have raised about CBP’s focus on high consequence
enforcement is the possibility that focusing scarce judicial and prosecutorial resources on
immigration enforcement diverts attention from more serious crimes.182 A 2013 Justice
Department study found that the number of immigration defendants in federal courts increased
664% between 1995 and 2010 (from 5,103 to 39,001); and that immigration cases accounted for
60% of the overall increase in pretrial detentions during that period.183 More generally,
immigration offenders accounted for 46% of federal arrests in 2010, outnumbering all other
crimes and up from 22% a decade earlier.184 A 2008 study by the Administrative Office of the
176 See CRS Report R42053, Fiscal Impacts of the Foreign-Born Population, by William A. Kandel. Although the
overall economic effects of migration—and unauthorized migration in particular—are difficult to estimate, research
suggests that fiscal costs of migration are disproportionately borne at the local level.
177 See, for example, Mark Harrison, “Beefed Up Border Patrol Jolts Farmers, Cows,” Seattle Times, November 13,
2011; Rafael Carranza, “Leaders Blame Lost Business Deals on Border Fence,” KGBT Channel 4 News, November 2,
2009, http://www.valleycentral.com/news/story.aspx?id=371266#.Tt0oAmNM8rs.
178 See, for example, Associated Press, “Quebec-Vermont Border Communities Divided by Post-9/11 Security,” CBC
News: Canada, August 14, 2011.
179 See, for example, NY School of Law, NY Civil Liberties Union, and Families for Freedom, Justice Derailed: What
Raids On New York’s Trains And Buses Reveal About Border Patrol’s Interior Enforcement Practices, New York:
November, 2011, http://www.nyclu.org/publications/report-justice-derailed-what-raids-trains-and-buses-reveal-about-
border-patrols-interi; Lornet Turnbull and Roberto Daza, “Climate of Fear Grips Forks Illegal Immigrants,” Seattle
Times, June 26, 2011.
180 See for example, American Civil Liberties Union, “Immigration Reform Should Eliminate Operation Streamline,”
http://www.aclu.org/files/assets/operation_streamline_issue_brief.pdf.
181 See for example, Alan Gomez, “Lawsuits Allege abuses by Border Patrol Agents,” USA Today, March 13, 2013;
Judith Greene and Alexis Mazón, “Privately Operated Federal Prisons for Immigrants: Expensive, Unsafe,
Unenecessary,” Justice Strategies, September 13, 2012; No More Deaths/No Mas Muertes, A Culture of Cruelty: Abuse
and Impunity in Short-Term U.S. Border Patrol Custody, 2011.
182 See, for example, National Immigration Forum, Operation Streamline: Unproven Benefits Outweighed by Costs to
Taxpayers, Washington, DC, September 2012.
183 Thomas H. Cohen, Special Report: Pretrial Detention and Misconduct in Federal District Courts, 1995-2010, U.S.
Department of Justice, Bureau of Justice Statistics, NCJ 239673, Washington, DC, February 2013.
184 Mark Motivans, Immigration Offenders in the Federal Justice System, 2010, U.S. Department of Justice, Bureau of
Justice Statistics, NCJ 238581, Washington, DC, July 2012.
Congressional Research Service
40
Border Security: Immigration Enforcement Between Ports of Entry
U.S. Courts found that while Congress had provided short-term funding to allow the courts to
respond to increased prosecutions, the courts faced a shortage of suitable courthouse and
detention facilities in some border locations.185
Effects on Regional Relations
What are the effects of U.S. border enforcement policies on U.S. relations with its continental
neighbors, Mexico and Canada? The United States and Canada have a strong record of
collaborative border enforcement, including through 15 binational, multi-agency Integrated
Border Enforcement Teams (IBETs) operating at 24 locations at and between U.S.-Canadian ports
of entry. In February 2011, President Obama and Prime Minister Harper signed the Beyond the
Border declaration, which described their shared visions for a common approach to perimeter
security and economic competitiveness; and the countries released an Action Plan on December
7, 2011, to implement the agreement.186 While some Canadians have raised objections to some of
the information sharing and joint law enforcement provisions of the agreement,187 border
enforcement between the ports has not been identified as a significant source of bilateral tension.
The United States and Mexico also cooperate extensively on border enforcement operations at the
Southwest border.188 Yet immigration enforcement occasionally has been a source of bilateral
tension. And with Mexicans being the most frequent target of U.S. immigration enforcement
efforts, some Mexicans have expressed concerns about the construction of border fencing, the
effects of border enforcement on migrant deaths, and the protection of unaccompanied minors
and other vulnerable groups, among other issues related to immigration enforcement.189
Conclusion: Understanding the Costs and Benefits
of Border Enforcement between Ports of Entry
The United States has focused substantial resources along its land borders to prevent and control
illegal migration since the 1980s, with investments in personnel, fencing, and surveillance assets
all up significantly in the post 9/11 period, in particular. Since 2005, CBP also has transformed its
approach to managing enforcement outcomes, through its Consequence Delivery System.
185 Administrative Office of the U.S. Courts, Report on the Impact on the Judiciary of Law Enforcement Activities
Along the Southwest Border, Washington, DC: Administrative Office of the U.S. Courts, July 2008.
186 DHS, “Beyond the Border Action Plan,” December 2011, http://www.dhs.gov/files/publications/beyond-the-border-
action-plan.shtm; also see CRS Report 96-397, Canada-U.S. Relations, coordinated by Ian F. Fergusson and Derek E.
Mix.
187 See for example, Dana Gabriel, “Toward a North American Police State and Security Perimeter: U.S.-Canada
‘Beyond the Border Agreement,’” Global Research, May 14, 2012.
188 See CRS Report R41349, U.S.-Mexican Security Cooperation: The Mérida Initiative and Beyond, by Clare Ribando
Seelke and Kristin Finklea.
189 See CRS Report R42560, Mexican Migration to the United States: Policy and Trends, by William A. Kandel, Clare
Ribando Seelke, and Ruth Ellen Wasem; Marc R. Rosenblum, Obstacles and Opportunities for Regional Cooperation:
The US-Mexico Case, Migration Policy Institute, April 2011, http://www.migrationpolicy.org/pubs/USMexico-
cooperation.pdf.
Congressional Research Service
41
Border Security: Immigration Enforcement Between Ports of Entry
Measuring the effects of border enforcement is difficult. On one hand, after reaching a high point
in 2000, Border Patrol apprehensions fell sharply in 2007-2011, reaching a 42-year low in
FY2011. The Border Patrol’s IDENT database also indicates a declining proportion of aliens is
apprehended more than once (i.e., recidivism is down). Estimates based on enforcement and
survey data and accounting for estimated apprehension and deterrence rates suggest that total
illegal inflows in 2009-2011 were well below levels observed in the two decades after IRCA’s
passage, but that illegal inflows increased somewhat in 2012.
On the other hand, there is also some evidence that migrants have adapted to more difficult
conditions at the border by using other means to enter the United States and by remaining longer.
A comprehensive accounting also may consider various potential unintended consequences of
border enforcement on the civil rights of legal residents and U.S. citizens in the border region, on
migrants’ human rights, on the quality of life in border communities, on the environment and
wildlife, and on U.S.-regional relations.
What do these findings mean for Members of Congress who oversee border security and
immigration policy? Especially in light of current fiscal constraints, some Members of Congress
may evaluate future border enforcement in terms of expected returns on America’s investments,
and they may consider the possibility that certain additional investments at the border may be met
with diminishing returns. Border infrastructure may offer an example: with 651 miles of fencing
and barriers already in place along the Southwest border, each additional mile would be in ever
more remote locations, and therefore more expensive to install and maintain and likely to deter
fewer unauthorized migrants. Similarly, some Members of Congress may question the concrete
benefits of deploying more sophisticated surveillance systems across the entire northern and
southern borders, including vast regions in which too few personnel are deployed to respond to
the occasional illegal entry that may be detected.
Deciding how to allocate border resources therefore requires a clear definition of the goals of
border security. Zero admissions of unauthorized migrants may not be a realistic goal when it
comes to migration control, as noted above, and is a higher standard than is expected of most law
enforcement agencies. While this report focuses on migration control at U.S. borders, border
security also encompasses the detection and interdiction of weapons of mass destruction (WMD),
narcotics, and other illicit goods; policies to combat human trafficking; and other security goals.
These diverse goals are often conflated in an undifferentiated debate about “border security”; but
each of these goals may suggest a different mix of border investments, as well as different metrics
and different standards for successful enforcement outcomes. Should policies to prevent
unauthorized migration be held to the same standards as policies to prevent the entry of WMDs,
for example?
Regardless of how these questions are answered in principle, debates about immigration control
and border security may benefit from better metrics of border security and illegal migration, and
from a more analytical approach to program design. The Border Patrol has taken a step in this
direction by analyzing recidivism data as a function of different enforcement outcomes through
its Consequence Delivery System. This report also identifies several metrics for measuring border
security, all of which have advantages and disadvantages. In the context of immigration policy
and a possible immigration reform bill, Members of Congress may choose to focus on the total
number of unauthorized aliens in the United States, in addition to border flows, since border
enforcement is just one of many factors (along with interior enforcement, visa policies, etc.)
influencing the size of the unauthorized population, and because more is known about the
population number than about border flows.
Congressional Research Service
42
Border Security: Immigration Enforcement Between Ports of Entry
Appendix. Capture-Recapture Methodology
The capture-recapture methodology for estimating unauthorized migration flows based on total
and recidivist alien apprehensions was first proposed by the sociologist Thomas Espenshade in
1995.190 Espenshade’s original model assumed that all intending migrants (i.e., everyone who
makes an initial crossing attempt) eventually succeed—an assumption supported by academic
research at the time.191 Likewise, the model focused exclusively on unauthorized Mexican
migrants, a population of particular interest since Mexicans represented 96% of all alien
apprehensions during the 1990s,192 and since Mexico’s long shared border with the United States
creates unique enforcement dynamics, including high recidivism rates.
The basic capture-recapture model works backwards from the total number of apprehensions and
recidivist apprehensions to calculate total illegal flow and the odds of apprehension. First, by
definition, the number of apprehensions is related to the total number of illegal crossings
multiplied by the probability of being apprehended on any given attempt. For example, if 1,000
aliens attempt to cross, and the probability of being apprehended on a given trip is 50%, then the
number of apprehensions would be 500. If unsuccessful migrants always make a second (and
subsequent) attempt to enter, the number of aliens making a second attempt is equal to number of
initial apprehensions (i.e., 500 in the previous example); and the number of apprehensions among
one-time repeat crossers would be 250. In the following period, 250 would attempt entry and 125
would succeed, and so on. By adding up these iterations, Espenshade shows that the total number
of apprehensions (A) is equal to the total flow of unauthorized aliens (F) times the odds of
apprehension, where odds are defined statistically as the probability of apprehension (P) divided
by one minus the probability of apprehension.193 Re-arranging this statement to solve for flow:
F = A/[P/(1-P)]
(1)
Second, the ratio of repeat apprehensions to total apprehensions is used to calculate the
probability of apprehension on a given attempt. In short, the formula for repeat apprehensions is
simply the formula for total apprehensions times the probability of being apprehended. As a
result, repeat apprehensions (R) divided by total apprehensions (A) yields the probability of
apprehension (Papprenehsion) on a given trip:194
Papprenehsion = R/A
(2)
The methodology used in this report adapts Espenshade’s model to account for the fact that some
aliens do not make a second or subsequent attempt after being apprehended—that is, that some
are deterred.195 This modified capture-recapture model also has been used in a 2013 Council on
190 Thomas J. Espenshade, “Using INS Border Apprehension Data to Measure the Flow of Undocumented Migrants
Crossing the U.S.-Mexico Frontier,” International Migration Review, vol. 29, no. 2 (Summer 1995), pp. 545-565.
191 Ibid., pp. 549-550.
192 CRS analysis of apprehensions data from DHS, Yearbook of Immigration Statistics FY2011, Washington, DC: DHS,
2012. Mexicans accounted for 90% of all apprehensions in 2000-2009, before falling to 83% in 2010 and 76% in
FY2011. (Mexicans represent a lower proportion of all apprehensions than of Border Patrol apprehensions; total
apprehensions data for FY2012 were not available when this report was released.)
193 Espenshade, “Using INS Border Apprehension Data,” pp. 551-552.
194 Ibid., p. 554.
195 The Consequence Delivery System seeks to reduce recidivism by increasing the proportion of aliens subject to
(continued...)
Congressional Research Service
43
Border Security: Immigration Enforcement Between Ports of Entry
Foreign Relations report;196 and DHS officials have indicated that DHS’s Border Conditions
Index, now under development, employs a similar method to estimate illegal flows between ports
of entry.197 In the modified model, the estimated probability of apprehension defined in equation
(2) is divided by one minus the probability of deterrence to calculate the probability of successful
enforcement (Penforcement):
Penforcement
=
(R/A)/(1-D)
(3)
Figure 9 in this report was generated by using equation (3) to estimate the probability of
successful enforcement at the Southwest border and equation (1) to estimate total Southwest
border illegal flows. In the absence of country-specific recidivism rates (and in light of the higher
costs to reentry following deportation of non-Mexicans), CRS’s analysis assumes non-Mexicans
do not re-enter in the same fiscal year. Thus, the calculations for equation (3) use CBP data on
total recidivists divided by CBP data on Mexican apprehensions to calculate a Mexico-specific
apprehension rate.198 Based on available survey and USBP turn back data, deterrence rates were
assumed to fall between 20 and 40%. CRS further assumed that Mexican and non-Mexican aliens
are apprehended at the same rate, and thus uses the value of P calculated in equation (3), along
with CBP data on total Southwest border apprehensions, to estimate total Southwest border illegal
inflows based on equation (1).
Author Contact Information
Lisa Seghetti
Section Research Manager
lseghetti@crs.loc.gov, 7-4669
Acknowledgments
Marc R. Rosenblum, a former CRS Specialist in Immigration Policy, was the original author of this report.
CRS Graphics Specialist Amber Hope Wilhelm prepared the figures for this report.
(...continued)
formal removal, criminal charges, and/or remote repatriation (see “CBP Consequence Delivery System”). And
unauthorized aliens from countries other than Mexico (i.e., 73% of USBP apprehensions in FY2012) typically are
deported to their home countries, substantially raising the cost of re-entry.
196 Roberts et al., Managing Illegal Immigration to the United States.
197 CBP Office of Congressional Affairs, December 20, 2011.
198 DHS also reportedly restricts its recidivism analysis to Mexican aliens, but may uses country-specific recidivism
data to calculate apprehension rates, and may therefore estimate a somewhat lower probability of successful
enforcement based on this methodology.
Congressional Research Service
44