Since May 2019, U.S.-Iran tensions have escalated significantly, but have not erupted into armed conflict. The Trump Administration, following its 2018 withdrawal from the 2015 multilateral nuclear agreement with Iran (Joint Comprehensive Plan of Action, JCPOA), has taken several steps in its campaign of applying "maximum pressure" on Iran. Iran and Iran-linked forces have attacked and seized commercial ships, caused destruction of some critical infrastructure in the Arab states of the Persian Gulf, and posed threats to U.S. forces and interests, including downing a U.S. unmanned aerial vehicle. Iran has reduced its compliance with the provisions of the JCPOA. The Administration has been deploying additional military assets to the region to try to deter future Iranian actions.
President Donald Trump has said he wants a diplomatic solution that would not only ease tensions but resolve broader disputes with Iran, centered on a revised JCPOA that encompasses not only nuclear issues but also Iran's ballistic missile program and Iran's support for regional armed factions. High-ranking officials from several countries have sought to mediate to try to de-escalate U.S.-Iran tensions by encouraging direct talks between Iranian and U.S. leaders. President Trump has stated that he welcomes talks with Iranian President Hassan Rouhani without preconditions, but no direct talks have been known to take place to date or are scheduled.
The United States - Iran tensions have the potential to escalate into significant conflict. The United States military has the capability to undertake a range of options against Iran, both against Iran directly and against its regional allies and proxies. Iran's materiel support for armed factions throughout the region, including its provision of short-range ballistic missiles to these factions, and Iran's network of agents in Europe, Latin America, and elsewhere, give Iran the potential to expand confrontation into areas where U.S. response options might be limited. A September 14, 2019, attack on critical energy infrastructure in Saudi Arabia demonstrated that Iran and/or its allies have the capability to cause significant damage to U.S. allies and to U.S. regional and global economic and strategic interests, and raised questions about the effectiveness of U.S. defense relations with the Gulf states in preventing future such Iranian attacks.
Members of Congress have received additional information from the Administration about the causes of the U.S.-Iran tensions and Administration responses. They have responded in a number of ways; some Members have sought to pass legislation requiring congressional approval for any decision by the President to take military action against Iran.
Additional detail on U.S. policy options on Iran, Iran's regional and defense policy, and Iran sanctions can be found in CRS Report RL32048, Iran: Internal Politics and U.S. Policy and Options, by Kenneth Katzman; CRS Report RS20871, Iran Sanctions, by Kenneth Katzman; CRS Report R44017, Iran's Foreign and Defense Policies, by Kenneth Katzman; and CRS Report R43983, 2001 Authorization for Use of Military Force: Issues Concerning Its Continued Application, by Matthew C. Weed.
U.S.-Iran relations have been mostly adversarial since the 1979 Islamic Revolution in Iran. U.S. officials and official reports consistently identify Iran's support for militant armed factions in the Middle East region a significant threat to U.S. interests and allies. Attempting to constrain Iran's nuclear program took precedence in U.S. policy after 2002 as that program advanced. The United States also has sought to thwart Iran's purchase of new conventional weaponry and development of ballistic missiles.
In May 2018, the Trump Administration withdrew the United States from the 2015 nuclear agreement (Joint Comprehensive Plan of Action, JCPOA), asserting that the accord did not address the broad range of U.S. concerns about Iranian behavior and would not permanently preclude Iran from developing a nuclear weapon.1 Senior Administration officials explain Administration policy as the application of "maximum pressure" on Iran's economy to (1) compel it to renegotiate the JCPOA to address the broad range of U.S. concerns and (2) deny Iran the revenue to continue to develop its strategic capabilities or intervene throughout the region.2 Administration officials deny that the policy is intended to stoke economic unrest in Iran.3
As the Administration has pursued its policy of maximum pressure, including imposing sanctions beyond those in force before JCPOA went into effect in January 2016, bilateral tensions have escalated significantly. Key developments that initially heightened tensions include the following.
Iran responded to the U.S. pressure in part by demonstrating its ability to harm global commerce and other U.S. interests and to raise concerns about Iran's nuclear activities. Iran might have sought to cause international actors, including those that depend on stable oil supplies, to put pressure on the Trump Administration to reduce its sanctions pressure on Iran.
In addition to direct Iranian action, Iran's allies in the region have been conducting attacks that might be linked to U.S.-Iran tensions, although it is not known definitively whether Iran directed or encouraged such attacks. Still, Trump Administration policy, as articulated by Secretary of State Pompeo, has been to hold Tehran responsible for the actions of its regional allies.13
On June 20, 2019, Iran shot down an unmanned aerial surveillance aircraft (RQ-4A Global Hawk Unmanned Aerial Vehicle) near the Strait of Hormuz, claiming it had entered Iranian airspace over the Gulf of Oman. U.S. Central Command officials stated that the drone was over international waters.20 IRGC commander-in-chief Major General Hossein Salami stated "The downing of the American drone is an open, clear and categorical message, which is: the defenders of the borders of Iran will decisively deal with any foreign aggression.... This is the way the Iranian nation deals with its enemies."
On June 20, 2019, according to his posts on the Twitter social media site, President Trump ordered a strike on three Iranian sites related to the Global Hawk downing, but called off the strike on the grounds that it would have caused Iranian casualties and therefore been "disproportionate" to the Iranian shootdown.21 The United States did reportedly launch a cyberattack against Iranian equipment used to track commercial ships.22
On July 18, 2019, President Trump announced that U.S. forces in the Gulf had downed an Iranian drone via electronic jamming in "defensive action" over the Strait of Hormuz. Iran denied that any of its drones were shot down.
An effort by the United Kingdom (UK) to enforce EU sanctions against Syria opened up a dispute between Iran and the UK.23 On July 4, authorities from the British Overseas Territory Gibraltar, backed by British marines, impounded an Iranian tanker, the Grace I, off the coast of Gibraltar on the grounds that it was allegedly violating an EU embargo on the provision of oil to Syria. Iranian officials termed the seizure an act of piracy, and in subsequent days, the IRGC Navy sought to intercept a UK-owned tanker in the Gulf, the British Heritage, but the force was reportedly driven off by a British warship. On July 19, the IRGC Navy seized a British-flagged tanker near the Strait of Hormuz, the Stena Impero, claiming variously that it violated Iranian waters, was polluting the Gulf, collided with an Iranian vessel, or that the seizure was retribution for the seizure of the Grace I.
On July 22, the UK's then-Foreign Secretary Jeremy Hunt explained the government's reaction to the Stena Impero seizure as pursuing diplomacy with Iran to peacefully resolve the dispute, while at the same time sending additional naval vessels to the Gulf to help secure UK commercial shipping. Secretary Hunt stated that the UK had "made clear in public that [it] would be content with the release of Grace I if there were sufficient guarantees the oil would not go to any entities sanctioned by the EU."24 President Donald Trump and other senior U.S. officials publicly supported the UK position. Secretary of State Pompeo said that "the responsibility ... falls to the United Kingdom to take care of their ships."25 At the same time, UK officials stated that they remained committed to the JCPOA and would not join the Trump Administration campaign of maximum pressure on Iran.
On August 15, following a reported pledge by Iran not to deliver the oil cargo to Syria, a Gibraltar court ordered the ship (renamed the Adrian Darya 1) released. Gibraltar courts turned down a U.S. Justice Department request to impound the ship as a violator of U.S. sanctions on Syria and on the IRGC, which the U.S. filing said was financially involved in the tanker and its cargo.26 The ship apparently delivered its oil to Syria despite the pledge27 and, as a consequence, the United States imposed new sanctions on individuals and entities linked to the ship and to the IRGC-linked network that the Department of the Treasury identified as assisting that and other Iranian oil shipments. On September 22, 2019, Iran released the Stena Impero.
Separate from the UK-Iran dispute over the Grace I and the Stena Impero, Iran seized an Iraqi tanker on August 5, 2019, for allegedly smuggling Iranian diesel fuel to "Persian Gulf Arab states."28
Parallels to Past Incidents in the Gulf29
Iran's apparent attacks on tankers in May and June share some characteristics with events in the mid-to-late 1980s during the 1980-1988 Iran-Iraq war. 1987-1988 represented the height of the "tanker war," in which both Iran and Iraq were attacking ships in the Gulf. The United States backed Iraq during that war, and sought to limit and deter Iranian attacks on shipping, but there were several U.S.-Iran skirmishes in the Gulf. To protect commercial shipping, the United States launched "Operation Earnest Will" in July 1987, in which the United States reflagged 11 of Kuwait's oil tankers and the U.S. Navy escorted them through the Gulf. Almost immediately after the operation began, one of the tankers, the Bridgeton, was damaged by a large contact mine laid by Iran. In August 1987, U.S. forces captured the Iran Ajr, an Iranian landing craft being used for covert minelaying. However, Iran continued attacking, including with missiles; on October 16, 1987, an Iranian Silkworm missile struck on a U.S.-flagged Kuwaiti tanker, Sea Isle City, 10 miles off Kuwait's Al Ahmadi port. In response to that attack, U.S. destroyers and Special Operations forces blew up an Iranian oil platform east of Bahrain. On April 14, 1988, an Iranian-laid mine struck the U.S. frigate Samuel B. Roberts on patrol in the central Gulf, an attack that led to an April 16, 1988, naval confrontation in which the United States, in Operation Praying Mantis, put a large part of Iran's naval force out of action, including sinking one of Iran's two frigates and rendering the other inoperable. On July 3, 1988, mistaking it for an attacking Iranian aircraft, the guided missile cruiser USS Vincennes shot down Iran Air commercial passenger flight 655, killing all aboard.
On September 14, an attack was conducted on multiple locations within critical Saudi energy infrastructure sites at Khurais and Abqaiq. The Houthi movement in Yemen, which receives arms and other support from Iran, claimed responsibility but Secretary of State Pompeo stated: "Amid all the calls for de-escalation, Iran has now launched an unprecedented attack on the world's energy supply. There is no evidence the attacks came from Yemen."31 Saudi officials said on September 16, 2019, that the attacks did not originate in Yemen and that the weapons used in the attack were of Iranian origin, but they did not name Iran as the perpetrator, instead inviting "U.N. and international experts ... to participate in the investigations."32 Press reports stated that U.S. intelligence indicates that Iran itself was the staging ground for the attacks, in which cruise missiles, possibly assisted by unmanned aerial vehicles, struck nearly 20 targets at those Saudi sites.33 Iranian officials have denied responsibility for the attack.
The attack shut down a significant portion of Saudi oil production and, whether conducted by Iran itself or by one of its regional allies, escalated U.S.-Iran and Iran-Saudi tensions and demonstrated a significant capability to threaten U.S. allies and interests. President Trump stated on September 16 that he would "like to avoid" conflict with Iran and the Administration did not retaliate militarily. U.S. officials did announce modest increases in U.S. forces in the region and some new U.S. sanctions on Iran. Secretary of State Pompeo visited Saudi Arabia and the UAE during September 18-19 to discuss responses to the attack, and in his press conferences in the region he stated an intent to use diplomacy to try to resolve the crisis.
The attacks on the Saudi infrastructure raised broader questions, including
Since the Trump Administration's May 2018 announcement that the United States would no longer participate in the JCPOA, Iranian officials repeatedly have rejected renegotiating the agreement or discussing a new agreement. Tehran also has conditioned its ongoing adherence to the JCPOA on receiving the agreement's benefits from the remaining JCPOA parties, collectively known as the "P4+1." On May 10, 2018, Iranian Foreign Minister Mohammad Javad Zarif wrote that, in order for the agreement to survive, "the remaining JCPOA Participants and the international community need to fully ensure that Iran is compensated unconditionally through appropriate national, regional and global measures." He added that
Iran has decided to resort to the JCPOA mechanism [the Joint Commission established by the agreement] in good faith to find solutions in order to rectify the United States' multiple cases of significant non-performance and its unlawful withdrawal, and to determine whether and how the remaining JCPOA Participants and other economic partners can ensure the full benefits that the Iranian people are entitled to derive from this global diplomatic achievement.35
Tehran also threatened to reconstitute and resume the country's pre-JCPOA nuclear activities.
Several meetings of the JCPOA-established Joint Commission since the U.S. withdrawal have not produced a firm Iranian commitment to the agreement.36 Tehran has argued that the remaining JCPOA participants' efforts have been inadequate to sustain the agreement's benefits for Iran. In May 8 letters to the other JCPOA participant governments, Iran announced that, as of that day, Tehran had stopped "some of its measures under the JCPOA," though the government emphasized that it was not withdrawing from the agreement. Specifically, Iranian officials said that the government will not transfer low enriched uranium (LEU) or heavy water out of the country in order to maintain those stockpiles below the JCPOA-mandated limits. A May 8 statement from Iran's Supreme National Security Council explained that Iran "does not anymore see itself committed to respecting" the JCPOA-mandated limits on LEU and heavy water stockpiles.37
Beginning in July 2019, the International Atomic Energy Agency (IAEA) verified that some of Iran's nuclear activities were exceeding JCPOA-mandated limits; the Iranian government has since increased the number of such activities.38 Specifically, according to IAEA reports, Iran has exceeded JCPOA-mandated limits on its heavy water stockpile, the number of installed centrifuges, its LEU stockpile, and the LEU's concentration of the relevant fissile isotope uranium-235. Tehran is also reportedly conducting JCPOA-prohibited research and development activities, as well as centrifuge manufacturing, and has also begun to enrich uranium at its Fordow enrichment facility.39 40
Iranian President Hassan Rouhani, in a November 5 speech, explained that Tehran still supports negotiations with the P4+1:
In the next two months, we still have a chance for negotiations. We will negotiate and talk with each other, and if we find the right solution, and the solution is in lifting of the sanctions, and that we will be able to sell our oil easily, we will be able to use our money in banks easily, and other issues that they have imposed sanctions on, such as metals and insurance, and if they lift sanctions fully, we will also return to the previous conditions fully.41
U.S. partner countries have generally backed U.S. charges of Iranian responsibility for the Iranian attacks discussed above. However, U.S. partner countries have consistently called for the de-escalation of tensions and the avoidance of war. The EU countries have said they will not join the U.S. maximum pressure campaign as a consequence of Iran's provocative acts, although the UK, France, and Germany have urged Iran to negotiate a new JCPOA that includes limits on Iran's missile development.42 Some U.S. allies have joined a U.S. effort to deter Iran from further attacks on shipping in the Gulf, discussed further below.
As tensions have increased with Iran, the Trump Administration has undertaken a number of steps to try to deter further attacks, weaken Iran strategically, and compel Iran to negotiate a broader resolution of U.S.-Iran differences.
To try to deter further Iranian attacks, the United States has added forces and military capabilities in the region, beyond the accelerated deployment of the USS Abraham Lincoln and associated forces, discussed above. The additional deployments as of October 2019 had added 14,000 thousand U.S. military personnel to a baseline of more than 60,000 U.S. forces in and around the Persian Gulf, which include those stationed at military facilities in the Arab states of the Gulf Cooperation Council (GCC: Saudi Arabia, Kuwait, UAE, Qatar, Oman, and Bahrain), and those in Iraq and Afghanistan.45 Defense Department officials indicated that the additional deployments have mostly restored forces who were redeployed from the region a few years ago, and do not represent preparation for any U.S. offensive against Iran.46
After several months in which tensions seemed stable or even declining, in late November 2019, the commander of U.S. Central Command, General Kenneth McKenzie, stated that the U.S. deployments during May—October might have deterred Iran from attacking U.S. targets, but that "I wouldn't rule [another Iranian attack like the September 14 attack on Saudi oil infrastructure] out going forward."52 Referring to recent rioting in Iran in response to a reduction in fuel subsidies, General McKenzie added that "Iran is under extreme pressure" and is trying to "crack the [maximum pressure] campaign" with attacks to provoke an American military response. In early December, press reports and U.S. officials provided details on the signs of Iranian activity of concern, including an Iranian shipment of sophisticated components for cruise and other short-range missiles bound for the Houthis but intercepted by U.S. naval forces on November 2553, and the reported Iranian supply of short range missiles to allied forces inside Iraq.54 A series of indirect fire attacks in December 2019 have targeted Iraqi military facilities where U.S. forces are present, amid ongoing protests and unrest in Iraq. The U.S. government has designated Iran-linked Iraqi groups and individuals in 2019 for involvement in human rights abuses and attacks on Iraqi protesters.55U.S. officials have said publicly that the attacks in Iraq were occurring with increased frequency and becoming more sophisticated.56
The identification of new Iranian threats—coupled with the CENTCOM assessment that the additional U.S. deployments were not sufficient to deter Iran—seems to have prompted consideration of deploying additional U.S. forces to the region. One report, denied by the Administration, said the Administration might send dozens more warships and as many as 14,000 more U.S. military personnel to the region57 At a Senate Armed Services Committee hearing on December 5, 2019, Undersecretary of Defense for Policy John Rood said that "as necessary, the secretary of Defense has told me he intends to make changes to our force posture there." But Rood did not say how large a potentially additional force the Pentagon may be considering. Cable News Network reported on December 5, 2019, citing conversations with unnamed DOD officials, that a more likely additional figure ranges from 4,000 to 7,000 personnel focused on air and missile defense.
In addition to deploying more U.S. forces, the Trump Administration has sought to assemble a coalition that would use military assets to try to protect commercial shipping in the Gulf. In June, Secretary Pompeo visited Saudi Arabia, UAE, and several Asian states to recruit allies to contribute funds and military resources to a new maritime security and monitoring initiative (termed "Operation Sentinel") for the Gulf, the Bab el-Mandeb Strait, and the Suez Canal. Defense Secretary Mark Esper told reporters on August 28, 2019, "I am pleased to report that Operation Sentinel is up and running," but the coalition, termed the International Maritime Security Construct (IMSC), was formally inaugurated in Bahrain in November 2019. It consists of seven nations (United States, UK, UAE, Saudi Arabia, Bahrain, Albania and Australia) operating four sentry ships at crucial points in the Gulf. 58Qatar and Kuwait have pledged to join the mission in the near future, and Canada and "some European countries" are described as having "expressed interest in the effort."59 The IMSC appears to supplement longstanding multilateral Gulf naval operations that have targeted smuggling, piracy, the movement of terrorists and weaponry, and other potential threats in the Gulf.
Additionally, Israeli Foreign Minister Yisrael Katz said Israel would join the coalition, although it is likely that Israel would remain in a supporting role in light of the stated opposition of Iran, Iraq, and other regional governments to a direct Israeli military role in the Gulf.60 Defense Department officials have not listed Israel as a participant in IMSC to date. China's ambassador to the UAE said in early August that China is considering joining the mission, although no announcement of China's participation has since been made.
France reportedly intends to lead a separate maritime security mission (headquartered in Abu Dhabi) in the Gulf starting in early 2020; the Netherlands and several other European countries have expressed interest. India has sent some naval vessels to the Gulf to protect Indian commercial ships.
Events could take any of several directions that might affect congressional oversight and authorization or limitations on the U.S. use of military force, Administration and congressional steps to support regional partners potentially affected by conflict, or new sanctions measures.
U.S. and Iranian officials have said they do not want armed conflict. However, leaders on each side have said they will respond with force if the other attacks.
The Iranian leadership insists that U.S. sanctions be eased, and, in order to pressure the United States to do so, Iran could undertake or provide material support for further actions such as the September 14 strike against Saudi critical energy infrastructure. Iran could potentially try to attack U.S. military, civilian, diplomatic, or other personnel. Iran could attack or seize additional commercial ships in the Gulf, possibly causing loss of life.
The IRGC's Qods Force (IRGC-QF) could encourage its allies in Syria, Lebanon,61 Iraq, Yemen, Bahrain, and Afghanistan to attack a wide range of targets, potentially including U.S. military personnel and installations.62 The IRGC-QF has supplied these regional allies with rockets, short-range ballistic missiles, and other weaponry to undertake such assaults.63 As one example, U.S. officials said in December 2019 that attacks on facilities in Iraq used by U.S. forces are increasing in frequency and sophistication, possibly to the point where U.S. forces would respond militarily, potentially causing escalation to U.S.-Iran conflict.64
For the past several years, the U.S. intelligence community, in its annual worldwide threat assessment briefings for Congress, has assessed that Iran has "the largest inventory of ballistic missiles in the region,"65 and the 2019 version of the annual, congressionally mandated report on Iran's military power by the Defense Intelligence Agency indicates that Iran is advancing its drone technology and the precision targeting of the missiles it provides to its regional allies.66 Israel asserts that these advances pose a sufficient threat to justify Israeli attacks against Iranian and Iran-allied targets in the region, including in Lebanon, Syria, and Iraq.67
The annual State Department report on international terrorism has consistently asserted that Iran and its key ally, Lebanese Hezbollah, have a vast network of agents in Europe, Latin America, and elsewhere that could act against U.S. personnel and interests outside the Middle East.68
It is possible that the U.S.-Iran tensions might not evolve to military conflict, but also might not result in talks that lead to a potential resolution of the U.S.-Iran differences. At the August 28, 2019, DOD press briefing discussed above, Defense Secretary Esper said: "I'm not sure I'm ready to call the crisis over yet, but so far so good. And we hope the trend lines continue that way." However, the September 14 attack and ongoing indirect fire attacks on facilities in Iraq indicate that the apparent stability could be upset suddenly.
U.S., U.S. partner, and Iranian officials have explored ways to de-escalate the tensions. It can be argued that a long-lasting compromise would require an easing pressure on Iran's economy and Iran's acceptance of some additional limits beyond those stipulated in the JCPOA. President Trump and other senior officials have stated repeatedly since May 2019 that the United States is willing to talk directly with Iranian leaders, without preconditions, to de-escalate tensions and negotiate a revised JCPOA.69
The United States and Iran do not have diplomatic relations and there have been no known high-level talks between Iran and Administration officials since the Trump Administration withdrew from the JCPOA. The absence of direct channels has led various third country leaders, such as Japanese Prime Minister Shinzo Abe, either with or separate from specific U.S. imprimatur, to try to move Tehran and Washington toward direct talks. President Trump confirmed on July 19, 2019, that he authorized Senator Rand Paul to engage in diplomatic discussions with Foreign Minister Zarif; Senator Paul reportedly met with Zarif in New York in July.70
Several Gulf countries have sent delegations to Iran to try to ease U.S.-Iran tensions that the Gulf leaders say could lead to severe destruction in the Gulf states themselves in the event of conflict.71 Whereas Qatar has consistently maintained relations with Iran, a UAE delegation that visited Tehran in late July undertook the first UAE security talks with Iran since 2013.
Prior to the September 14 attack on Saudi energy infrastructure, French President Macron produced apparent movement toward U.S.-Iran talks. While hosting the G-7 summit in Biarritz, Macron invited Foreign Minister Zarif to meet with him and to speak with British and German diplomats. No Trump-Zarif meeting took place in Biarritz but, at a press conference at the close of the summit, President Trump reiterated his willingness, in principle, to meet with Iranian President Hassan Rouhani, presumably during the U.N. General Assembly meetings in New York in September.
Some press reports indicated that President Trump considered supporting a French credit line proposal discussed below by approving sanctions waivers and exceptions to facilitate the credit line, possibly as an incentive for Iran to meet with him.72 However, in the wake of the September 14 attacks in Saudi Arabia and since, the Supreme Leader has stated that there would be no U.S.-Iran talks and Rouhani and Zarif have restated the view that U.S. sanctions be lifted before any such talks.
Absent U.S.-Iran talks, the EU or other actors could also produce a de-escalation by formulating policies that provide Iran with the economic benefits of the JCPOA. One new European proposal was revealed at the G-7 meeting—a proposal under which multiple countries would provide a $15 billion credit line, secured by future deliveries of oil, in exchange for Iran's return to full JCPOA compliance. The credit line would facilitate operations of an EU trading vehicle (Instrument in Support of Trading Exchanges, INSTEX) that has yet to complete any transactions but that attracted several new European partners in November 2019.73
The military is a tool of national power that the United States can use to advance its objectives, and the design of a military campaign and effective military options depend on the policy goals that U.S. leaders seek to accomplish. The Trump Administration has stated that its "core objective ... is the systemic change in the Islamic Republic's hostile and destabilizing actions, including blocking all paths to a nuclear weapon and exporting terrorism."74 As such, the military could be used in a variety of ways to try and contain and dissuade Iran from prosecuting its "hostile and destabilizing actions." These ways range from increasing presence and posture in the region to use of force to change Iran's regime. As with any use of the military instrument of national power, any employment of U.S. forces in this scenario could result in retaliatory Iranian action and/or the escalation of a crisis.
U.S. military action may not be the appropriate tool to achieve systemic change within the Iranian regime, and may in fact set back the political prospects of Iranians sympathetic to a change of regime. Employing overt military force is likely to strengthen anti-American elements within the Iranian government. Some observers question the utility of military power against Iran due to global strategic considerations. The 2017 National Security Strategy and 2018 National Defense Strategy both note that China and Russia represent the key strategic challenges to the United States today and into the future. As such, shifting military assets into the United States Central Command (CENTCOM) area of responsibility requires diverting them from use in other theaters such as Europe and the Pacific, thereby sacrificing other long-term U.S. strategic priorities.
Secretary of Defense Mark Esper and other U.S. officials have stated that the additional U.S. deployments since May are intended to deter Iran from taking any further provocative actions and position the United States to defend U.S. forces and interests in the region.75 Iranian attacks after previous U.S. deployments could be viewed to suggest that deploying additional assets and capabilities might not necessarily succeed in deterring Iran from using military force.
On the other hand, there are risks to military inaction that might potentially outweigh those associated with the employment of force. For example, should Iran acquire a nuclear weapons capability, U.S. options to contain and dissuade it from prosecuting hostile activities could be significantly more constrained than they are at present.76
For illustrative purposes only, below are some potential additional policy options related to the possible use of military capabilities against Iran, beyond the IMSC discussed above. Not all of these options are mutually exclusive, nor do they represent a complete list of possible options, implications, and risks. And, the Congress has assessed its role in any decisions regarding whether to undertake military action against Iran, as discussed later in this report. The following discussion is based entirely on open-source materials.
Without a more detailed articulation of how the military might be employed to accomplish U.S. objectives vis-a-vis Iran, and a reasonable level of confidence about how any conflict might proceed, it is difficult to assess with any precision the likely fiscal costs of a military campaign, or even just heightened presence. Still, any course of action listed in this report is likely to incur significant additional costs. Factors that might influence the level of expenditure required to conduct operations include, but are not limited to, the following:
At the same time, there is potential for some U.S. costs to be offset by contributions. The Persian Gulf states and other countries have a track record of offsetting U.S. costs for Gulf security. In the current context, President Trump stated in October 2019 that Saudi Arabia would pay for the deployment of additional U.S. troops and capabilities to assist with the territorial defense of Saudi Arabia and the deterrence of Iranian aggression in the region overall, and subsequent reports indicate that U.S. and Saudi officials are negotiating a cost-sharing arrangement for the new deployments.82
In June 2019, amidst attacks against tankers in the Gulf of Oman and Iran's shootdown of a U.S. military drone, some Members expressed concern about the legal justification for military operations in or against Iran. On June 22, Senator Bernie Sanders cast doubt on the notion of a "limited strike," saying that "[attacking] another country with bombs ... that's an act of warfare" and said that an attack on Iran would be, in his view, "unconstitutional."83 Other Members positioned themselves as more generally supportive of broad discretion for the Administration to act. Senator Tom Cotton said on June 16 that "these unprovoked attacks on commercial shipping warrant a retaliatory military strike" and argued that the President had the authority to order such an attack.84 The day before, Senator Lindsey Graham made a similar argument, stating that "enough is enough" and called on President Trump to "be prepared to make Iran pay a heavy price by targeting their naval vessels and, if necessary, their oil refineries."85
President Trump said in a June 24 interview that he believes he has the authority to direct strikes against Iran, and said, "I do like keeping them [Congress] abreast, but I don't have to do it, legally."86 On June 25, he tweeted that "any attack by Iran on anything American will be met with great and overwhelming force. In some areas, overwhelming will mean obliteration."87
The prospect of U.S. military action against Iran in the wake of the September attacks on Saudi oil facilities at Abqaiq and Khurais prompted additional responses from several Members of Congress. President Trump's statement that the United States was "locked and loaded" but "waiting to hear from the Kingdom as to who they believe was the cause of this attack, and under what terms we would proceed" drew particular congressional attention, with several Members emphasizing, as Representative Cicilline wrote, that "If the President wants to use military force, he needs Congress—not the Saudi royal family—to authorize it."88 Other Members, while generally backing the Administration's assessment that Iran was behind the attacks, argued that time should be given to verify intelligence conclusions.89 Senator Graham described the attack on Abqaiq and Khurais as "literally an act of war" that Iran committed because it interpreted the President's decision to call off airstrikes in response to the June drone shootdown as a "sign of weakness"; President Trump rejected that characterization, describing his approach as "a sign of strength that some people just don't understand!"90
The buildup of U.S. forces in the region in response to Iranian activities has also attracted congressional attention. At a December 5, 2019, hearing with Under Secretary of Defense for Policy John Rood, Senator Josh Hawley said the Pentagon had "made multiple contradictory public statements" with regard to reports of additional U.S. force deployments. Senator Hawley also pressed Under Secretary Rood on "what it is exactly that we're aiming to deter," arguing that "regional stability and the absence of an attack on American forces are…very different" and that "if our aim is to prevent all conflict in the region, we're going to be sending a lot more than 14 or 28 or 100,000 ground troops."91 Section 1227 of the FY2020 National Defense Authorization Act (S. 1790), which has been reported out by the conference committee on the legislation and passed by the House, would require an Administration report to Congress on diplomatic and military channels of deconfliction with Iran to "prevent miscalculation" that could "lead to unintended consequences, including unnecessary or harmful military activity."
Although Presidents have long asserted wide-ranging authority to unilaterally initiate the use of military force, no legislation has been enacted authorizing the use of force against Iran, and several measures include provisions specifying that such authorization is not being granted.92 For instance, Section 9026 of Division C of H.R. 2740 (the Department of Defense Appropriations Act, 2020), as engrossed in the House on June 19, 2019, would state that "Nothing in this Act may be construed as authorizing the use of force against Iran." H.R. 2500, the National Defense Authorization Act for FY2020, as reported in the House on June 19, 2019, contains a similar provision (Section 1225). On July 12, 2019, the House also passed, by a vote of 251-170, an amendment to H.R. 2500 that would prohibit funding for the use of force against Iran, with provisions clarifying that such a prohibition would not prevent the President from using necessary and appropriate force to defend U.S. allies and partners, consistent with the War Powers Resolution. Neither provision was included in the conference report, as passed by the House in December 2019.
On June 28, 2019, the Senate rejected by a 50-40 vote an amendment (S.Amdt. 883) to the FY2020 National Defense Authorization Act that would have prohibited the use of any funds to "conduct hostilities against the Government of Iran, against the Armed Forces of Iran, or in the territory of Iran, except pursuant to an Act or joint resolution of Congress specifically authorizing such hostilities."93
At a Senate Foreign Relations Committee hearing on April 10, 2019, Secretary of State Pompeo, when asked if the Administration considers the use of force against Iran as authorized, answered that he would defer to Administration legal experts on that question. However, he suggested that the 2001 authorization for use of military force (AUMF, P.L. 107-40) against those responsible for the September 11 terrorist attacks could potentially apply to Iran, asserting that "[Iran has] hosted Al Qaida. They have permitted Al Qaida to transit their country. [There's] no doubt there is a connection between the Islamic Republic of Iran and Al Qaida. Period. Full stop." Other analyses have characterized the relationship between Iran and Al Qaeda as "an on-again, off-again marriage of convenience pockmarked by bouts of bitter acrimony."94 As passed by the House, Section 9025 of H.R. 2740 would repeal the 2001 AUMF within 240 days of enactment.95
In a June 28, 2019, letter to House Foreign Affairs Committee Chairman Eliot Engel, Assistant Secretary of State for Legislative Affairs Mary Elizabeth Taylor stated that "the Administration has not, to date, interpreted either [the 2001 or 2002] AUMF as authorizing military force against Iran, except as may be necessary to defend U.S. or partner forces engaged in counterterrorism operations or operations to establish a stable, democratic Iraq." In response, Chairmen Engel and Middle East Subcommittee Chairman Ted Deutch welcomed the Administration's apparent acknowledgment that "the 2001 and 2002 war authorizations do not apply to military action against Iran," but cautioned that "the Administration claims that the President could use these authorizations to attack Iran in defense of any third party he designates a partner."96 In reviewing the letter, two analysts have suggested additional related topics for potential congressional oversight, including which groups are carrying out such counterterrorism operations, where they are doing so, and what nations or groups threaten them.97
Additionally, some Members seeking to prevent the Administration from pursuing military action against Iran have introduced several standalone measures prohibiting the use of funds for such operations, such as the Prevention of Unconstitutional War with Iran Act of 2019 (H.R. 2354/S. 1039) which would prevent the use of any funds for "kinetic military operations in or against Iran" except in case of an imminent threat.
Given ongoing tensions with Iran, Members are likely to continue to assess and perhaps try to shape the congressional role in any decisions regarding whether to commit U.S. forces to potential hostilities. In assessing its authorities in this context, Congress might consider, among other things, the following:
Conflict with, or increased military activity in or around, Iran could generate significant costs, financial and otherwise. With that in mind, Congress could consider the following:
Sources: Created by CRS using data from the U.S. Department of State, ESRI, and GADM.
Source: CRS. Based on, and includes, map by Navy of the United Kingdom.
Author Contact Information
For information on the JCPOA and the rationale for the U.S. withdrawal, see CRS Report R43333, Iran Nuclear Agreement and U.S. Exit, by Paul K. Kerr and Kenneth Katzman.
Speech by Secretary of State Michael Pompeo, Heritage Foundation, May 21, 2018; Testimony of Ambassador Brian Hook before the House Foreign Affairs Subcommittee on Middle East, North Africa, Hearing on U.S.-Iran Relations. June 19, 2019.
Speech by Secretary of State Pompeo, Heritage Foundation, op. cit.
Statement from the President on the Designation of the Islamic Revolutionary Guard Corps as a Foreign Terrorist Organization, April 8, 2019, at https://www.whitehouse.gov/briefings-statements/statement-president-designation-islamic-revolutionary-guard-corps-foreign-terrorist-organization/.
Department of State, Office of the Spokesperson, Factsheet: Designation of the Islamic Revolutionary Guard Corps, April 8, 2019.
State Department Factsheet, April 22, 2019, at https://www.state.gov/advancing-the-u-s-maximum-pressure-campaign-on-iran/.
Letter from Mary Elizabeth Taylor, Assistant Secretary of State for Legislative Affairs, to Senator James Risch, Chairman of the Senate Foreign Relations Committee. May 3, 2019.
The text of the announcement can be found at https://www.whitehouse.gov/briefings-statements/statement-national-security-advisor-ambassador-john-bolton-2/.
Letter from Secretary of State Michael R. Pompeo to Senate Foreign Relations Committee Chairman James E. Risch, May 24, 2019.
Department of Defense Briefing on Iran, May 24, 2019. For analysis on Saudi Arabia, see CRS Report RL33533, Saudi Arabia: Background and U.S. Relations, by Christopher M. Blanchard.
Pamela Falk, "Oil tanker attack probe reveals new photos, blames likely 'state actor,'" CBS News, June 7, 2019.
Statement by the Secretary of State, June 13, 2019.
Pompeo Warns Iran about Trigger for U.S. Military Action as Some in Administration Question Aggressive Policy. Washington Post, June 18, 2019.
For analysis on Iraq, see CRS Report R45025, Iraq: Background and U.S. Policy, by Christopher M. Blanchard.
Department of Defense Briefing on Iran. May 24, 2019, op. cit.
"Rockets strike near U.S.-linked oil installation and military bases in Iraq; 3 wounded," Washington Post, June 19, 2019.
"U.S. says Saudi pipeline attacks originated in Iraq: Wall Street Journal," Reuters, June 28, 2019. For analysis on the Yemen conflict, see CRS Report R43960, Yemen: Civil War and Regional Intervention, by Jeremy M. Sharp.
Sadursan Raghavan, "Yemeni rebels claim new drone attack on Saudi airport," Washington Post, June 17, 2019.
"The Taliban Claimed an Attack on U.S. Forces. Pompeo Blamed Iran," Washington Post, June 16, 2019.
See U.S. Central Command Statement at https://www.centcom.mil/MEDIA/STATEMENTS/Statements-View/Article/1881682/us-central-command-statement-iranians-shoot-down-us-drone/.
President Donald Trump interview on "Meet the Press," June 23, 2019.
"U.S. Cyberattack made it Harder for Iran to Target Oil Tankers." New York Times, August 29, 2019.
British-Flagged Tanker Leaves Iran, Two Months After It Was Seized. New York Times, September 27, 2019.
UK Foreign and Commonwealth Office, Statement by Jeremy Hunt to Parliament, July 22, 2019.
"In naval confrontation with Iran, great Britain can find neither ships nor friends," Defense News, July 25, 2019.
"Iran Warns U.S. Against Seizing Oil Tanker Headed to Greece." Bloomberg, August 18, 2019.
Iran Tanker Unloaded its Cargo, Tehran Says. New York Times, September 10, 2019.
"Iran Reportedly Seizes Iraqi Tanker In Persian Gulf." NPR, August 5, 2019.
Much of this textbox is derived from Ronald O'Rourke, U.S. Naval Institute Proceedings, "The Tanker War," May 1988; and CRS Issue Brief IB87145, "Persian Gulf: U.S. Military Operations," January 19, 1989.
For more detail on the attacks and implications, see CRS Insight IN11167, Attacks Against Saudi Oil Rattle Markets, by Michael Ratner, Christopher M. Blanchard, and Heather L. Greenley and CRS Report RL33533, Saudi Arabia: Background and U.S. Relations, by Christopher M. Blanchard.
Secretary Pompeo on Twitter. 3:59 PM, September 14, 2019.
Kingdom of Saudi Arabia Ministry of Foreign Affairs Statement. September 16, 2019.
U.S. Tells Saudi Arabia Oil Attacks Were Launched from Iran." Wall Street Journal, September 16, 2019.
This section was prepared by Paul K. Kerr. Specialist in Nonproliferation. For additional details, see CRS Report RL34544, Iran's Nuclear Program: Status, by Paul K. Kerr.
"Letter of Foreign Minister to UN Secretary General," May 10, 2018.
Unless otherwise noted, this paragraph is based on "AEOI Chief: Iran No More Remaining Restricted To 300 Kg Ceiling For Enriched Uranium," Fars News Agency, May 8, 2019; "Iran: Report Publishes Text of Supreme National Security Council Statement on Nuclear Deal," Tehran Fararu Online, May 8, 2019; Revision: Iran: President Ruhani Heralds New Nuclear Deal Strategy, Announces 60-Day Deadline, May 8, 2019; Statement from Supreme National Security Council of the Islamic Republic of Iran, May 8, 2019; "Spokesman: Iran to Cross 300kg Uranium Stockpile Borderline in 10 Days," FARS News Agency, June 17, 2019.
"Parliament Speaker's Top Advisor: Iran Not to Extend 60-Day N. Deal Deadline," FARS News Agency, June 16, 2019.
Unless otherwise noted, this paragraph is based on the following sources: Verification and Monitoring in the Islamic Republic of Iran in Light of United Nations Security Council Resolution 2231 (2015), Report by the Director General, GOV/INF/2019/8, July 1, 2019; Verification and Monitoring in the Islamic Republic of Iran in Light of United Nations Security Council Resolution 2231 (2015), Report by the Director General, GOV/INF/2019/9, July 8, 2019; Verification and Monitoring in the Islamic Republic of Iran in Light of United Nations Security Council Resolution 2231 (2015), Report by the Acting Director General, GOV/2019/32, August 30, 2019. Verification and Monitoring in the Islamic Republic of Iran in Light of United Nations Security Council Resolution 2231 (2015), Report by the Acting Director General, GOV/2019/55, November 11, 2019; Verification and Monitoring in the Islamic Republic of Iran in Light of United Nations Security Council Resolution 2231 (2015), Report by the Acting Director General, GOV/INF/2019/17, November 18, 2019.
The JCPOA prohibits Iran from enriching uranium at this facility.
The remaining JCPOA participants apparently judge Tehran in compliance with the agreement. For additional details, see CRS Report R40094, Iran's Nuclear Program: Tehran's Compliance with International Obligations, by Paul K. Kerr.
"Iran President Announces Fourth Step in Scaling Back Nuclear Commitments–Text," November 7, 2019 (Text of speech by Iranian President Hassan Rouhani at opening ceremony for Azadi Innovation Factory in Tehran published by website of the Presidency of the Islamic Republic of Iran, November 5, 2019).
European powers back U.S. in blaming Iran for Saudi oil attack, urge broader talks. Reuters, September 23, 2019.
For additional detail on U.S. sanctions, see CRS Report RS20871, Iran Sanctions, by Kenneth Katzman.
The text of the Order can be found at https://www.whitehouse.gov/presidential-actions/executive-order-imposing-sanctions-respect-iron-steel-aluminum-copper-sectors-iran/.
Paul Sonne and Missy Ryan, "Amid tensions with Iran, White House mulls U.S. military request to send more forces to the Middle East," Washington Post, May 23, 2019; DOD Statement on Deployment of Additional U.S. Forces and Equipment to the Kingdom of Saudi Arabia. October 11, 2019.
Gordon Lubold and Michael Gordon, "U.S. Deploys Forces to Mideast to Mideast to Deter Iran," Wall Street Journal, May 5, 2019.
Department of Defense Briefing on Iran, May 24, 2019, op. cit.
Doha Madani, "U.S. Sending 1,000 troops to Middle East amid heightened tension with Iran," NBC, June 18, 2019.
Robert Burns, "Officials: US putting troops back in Saudi Arabia," Associated Press, July 21, 2019.
DOD Statement on Deployment of U.S. Forces and Equipment to the Kingdom of Saudi Arabia. September 26, 2019.
DOD Statement on Deployment of Additional U.S. Forces and Equipment to the Kingdom of Saudi Arabia. October 11, 2019.
U.S. Commander Warns of Iranian Attack in Middle East. New York Times, November 23, 2019.
Reuters, December 5, 2019; On the Record Briefing by Special Representative for Iran and Senior Advisor to the Secretary Brian Hook. December 5, 2019.
Iran is Secretly Moving Missiles into Iraq, U.S. Officials Say. New York Times, December 4, 2019; U.S. Warship in the Gulf Seizes Alleged Iranian Missile Parts. Al Jazeera English, December 5, 2019.
"Iraqi security forces wounded in rocket attack near Baghdad airport." Washington Post, December 9, 2019.
"U.S. Official Warns of Iran-Backed Attacks in Iraq Leading to Uncontrollable Escalation." Asharq Al Awsat, December 11, 2019.
Trump Administration Considers 14,000 More Troops for Mideast. Wall Street Journal, December 4, 2019.
Department of Defense. International Unit Serves Critical Role in Persian Gulf. November 25, 2019.
See "Israel to join US-led coalition in Persian Gulf." Anadolu Agency, August 7, 2019.
For analysis on Syria and on Lebanon see CRS Report RL33487, Armed Conflict in Syria: Overview and U.S. Response, coordinated by Carla E. Humud and CRS Report R44759, Lebanon, by Carla E. Humud.
"Iran's Playbook—Deconstructing Tehran's Regional Strategy," Soufan Center, May 2019, at https://thesoufancenter.org/irans-playbook-deconstructing-tehrans-regional-strategy-by-the-soufan-center/.
Ambassador Brian Hook, "The Iranian Regime's Transfer of Arms to Proxy Groups," November 29, 2018.
"U.S. Official Warns of Iran-Backed Attacks in Iraq Leading to Uncontrollable Escalation." Asharq Al Awsat, December 11, 2019.
Senate Select Committee on Intelligence. Worldwide Threat Assessment of the U.S. Intelligence Community. January 29, 2019.
The report can be accessed at https://www.dia.mil/Portals/27/Documents/News/Military%20Power%20Publications/Iran_Military_Power_LR.pdf
"As Israel's anti-Iran strategy shifts into higher gear, worries of fresh conflict grow."Al Monitor, September 13, 2019.
Department of State. Country Reports on Terrorism: 2018. Released October 2019.
Alyza Sebenius, "Trump Says 'Always a Chance' of War with Iran But Prefers Talks," Bloomberg, June 5, 2019.
"Trump: Sen. Rand Paul to help with Iran negotiations," Politico, July 19, 2019.
"Iran, U.A.E. Discuss Maritime Security amid Heightened Tensions in Gulf." Wall Street Journal, July 30, 2019.
"Bolton's departure allegedly pegged to disagreement over lifting sanctions on Iran." Washington Post, September 14, 2019.
"France reportedly offers Iran $15bn Instex credit line for sanctions-protected trade." Intellinews, August 7, 2019.
The White House, A Look at the U.S. Strategy for Iran, February 13, 2019, at https://www.whitehouse.gov/articles/look-u-s-strategy-iran/.
DOD Statement on Deployment of Additional U.S. Forces and Equipment to the Kingdom of Saudi Arabia, October 11, 2019; "U.S. Military has Enough Capability in the Middle East for Now: Esper," Reuters, December 9, 2019.
Kathleen J. McInnis (2005) Extended deterrence: The U.S. credibility gap in the Middle East, The Washington Quarterly, 28:3, 169-186, DOI: 10.1162/0163660054026489.
"Trump Administration Prepares Multiple Military Options for Iran, Including Airstrikes and Setting Up Ground Invasion." Newsweek, May 14, 2019.
Emanuele Ottolenghi, "Only Crippling Sanctions Will Stop Iran," New York Times, March 2, 2012.
Eric Schmitt and Julian Barnes, "White House Reviews Military Plans against Iran, in Echoes of Iraq War," New York Times, May 13, 2019.
Adam Taylor, "A conflict with Iran would not be like the Iraq War. It would be worse," Washington Post, May 14, 2019.
IISS, The Military Balance: 2019, Iran.
"Pentagon Advances Talks to Set Terms for Expanding Saudi Defense Mission." Washington Post, November 28, 2019.
Grace Segers, "Bernie Sanders says Trump 'helped create the crisis' in Iran," CBS News, June 22, 2019.
Nicholas Wu, "Trump says he doesn't want war, but Sen. Cotton called for 'retaliatory strikes' on Iran," USA Today, June 16, 2019.
Lindsey Graham, Twitter, June 15, 2019. https://twitter.com/LindseyGrahamSC/status/1140063250438078466.
Saagar Enjeti and Jordan Fabian, "EXCLUSIVE: Trump: I do not need congressional approval to strike Iran," The Hill, June 24, 2019.
President Trump (@realDonaldTrump), Twitter, June 25, 2019, 7:42 AM.
John Bennett, "Democrats object to Trump's threatening Iran over Saudi oil attack," Roll Call, September 16, 2019.
Joe Gould, "Senate Republicans not ready for US military action against Iran," Defense News, September 17, 2019.
Caroline Kelly, "Trump rebuts Graham: My response to Iran 'was a sign of strength,'" CNN, September 18, 2019.
Senate Armed Services Committee Holds Hearing on National Defense Strategy Implementation, CQ Congressional Transcripts, December 5, 2019.
Some analysts have suggested that the 1973 War Powers Resolution (P.L. 93-148), which requires the President to notify Congress when U.S. armed forces are introduced into hostilities or situations of imminent hostilities and withdraw those forces within 60 to 90 days unless Congress authorizes such action, might also represent a check on the President's authority under Article II of the Constitution. Scott Anderson, "When Does the President Think He Can Go To War With Iran?" Lawfare, June 24, 2019. For more, see CRS Report R42699, The War Powers Resolution: Concepts and Practice, by Matthew C. Weed.
For more on arguments around congressional attempts to limit military action via appropriations, see CRS Report R41989, Congressional Authority to Limit Military Operations, by Jennifer K. Elsea, Michael John Garcia, and Thomas J. Nicola.
Ned Price, "Why Mike Pompeo Released More bin Laden Files," Atlantic, November 8, 2017. See also Barbara Slavin, "Expediency and betrayal: Iran's relationship with al-Qaeda," Al-Monitor Iran Pulse, September 7, 2018.
For background, see CRS Report R43983, 2001 Authorization for Use of Military Force: Issues Concerning Its Continued Application, by Matthew C. Weed.
Engel & Deutch Receive State Department Answer on Old War Authorizations & Iran, Committee on Foreign Affairs Press Release, June 28, 2019. While the Trump Administration has previously stated that it views the 2001 AUMF as authorizing U.S. action in defense of partner forces participating in counter-Islamic State operations in Syria, one analyst argues that the State Department's letter represents "the first time the executive branch has publicly extended this collective self-defense theory to the 2002 AUMF." Scott R. Anderson, "Parsing the State Department's Letter on the Use of Force Against Iran," Lawfare, July 3, 2019.
Tess Bridgeman and Ryan Goodman, "Unpacking the State Dept Acknowledgment that 2001 and 2002 AUMFs Don't Authorize War Against Iran," Just Security, July 3, 2019.