UPDATED: Recent U.S. Airstrikes: Legal Authorities and Questions

UPDATED: Recent U.S. Airstrikes: Legal Authorities and Questions

Legal Sidebari

UPDATED: Recent U.S. Airstrikes: Legal
Authorities and Questions
Updated February 18, 2020
Update: The Trump Administration has reported to Congress a “change in application of the existing
legal and policy frameworks” regarding the use of military force, which presented the following legal
justification for the January airstrikes:
Article II of the United States Constitution, empowers the President, as Commander in Chief, to
direct the use of military force to protect the Nation from an attack or threat of imminent attack and
to protect important national interests. Article II thus authorized the President to use force against
forces of Iran, a state responsible for conducting and directing attacks against United States forces
in the region. In addition, under the 2002 Authorization for Use of Military Force Against Iraq
(2002 AUMF), “the President is authorized to use the Armed Forces of the United States as he
determines to be necessary and appropriate in order to ... defend the national security of the United
States against the continuing threat posed by Iraq.” Although the threat posed by Saddam Hussein's
regime was the initial focus of the statute, the United States has long relied upon the 2002 AUMF
to authorize the use of force for the purpose of establishing a stable, democratic Iraq and addressing
terrorist threats emanating from Iraq. Such uses of force need not address threats from the Iraqi
Government apparatus only, but may address threats to the United States posed by militias, terrorist
groups, or other armed groups in Iraq. (Footnotes omitted).
The House Committee on Foreign Affairs posted this report on its website on February 14, 2020. The
original Legal Sidebar from January 8, 2020 appears below.
Recent U.S. airstrikes in Iraq and Syria have raised legal questions concerning the scope of the
President’s power to use force against Iran and Iran-backed organizations. In late December, U.S. forces
conducted airstrikes against five facilities in Iraq and Syria used by Kata’ib Hizbollah—an entity with ties
to Iran designated by the Department of State as a foreign terrorist organization. According to a
Department of Defense (DOD) statement, the strikes came in response to attacks on military bases in Iraq
that host U.S. forces engaged in the campaign to defeat the Islamic State. Two days later, Kata’ib
Hizbollah supporters and others marched to the U.S. Embassy in Baghdad, damaging property and setting
fire to outer buildings. Then, on January 2, 2020, the U.S. military, at the direction of the President, killed
Qasem Soleimani, the head of the Islamic Revolutionary Guard Corps-Quds Force (IRGC-QF) and Abu
Mahdi al Muhandis, an Iraqi security official and Kata’ib Hizballah founder named as a specially
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designated global terrorist by the U.S. government. According to a DOD statement, Soleimani “approved”
the attack on the U.S. Embassy in Baghdad and was “actively developing” plans to attack American
diplomats and service members in the region. The Secretary of State described the threats as “imminent,”
but did not publicly offer specific information.
According to media outlets, the President described the legal bases for the Soleimani strike in a fully
classified letter under the War Powers Resolution (a 1973 law detailed in this CRS Report). While the
letter’s text has not been made public, media outlets reported that National Security Advisor Robert
O’Brien made the following on-the-record statement concerning the legal authority for the strike:
It was a fully authorized action under the 2002 [Authorization for Use of Military Force (AUMF)]
and is consistent with his constitutional authority as commander in chief to defend our nation and
our forces against [an] attack like those that Soleimani has directed in the past and was plotting now.
This Sidebar examines the President’s domestic legal authority to initiate military action under the two
sources cited in the National Security Advisor’s statement: the Constitution and the 2002 authorization for
use of military force related to Iraq (2002 AUMF). Although not discussed in O’Brien’s statement, this
Sidebar also examines the implications of the ban on assassinations in Executive Order 12333 as well as
the international legal framework governing the strikes.
Did the President Have Constitutional Authority for the Strikes?
As discussed in this CRS InFocus, the Constitution purposefully divides war powers between Congress
and the President. The Supreme Court has made clear that the President has the constitutional power to
defend the nation from an armed attack or insurrection within its borders without congressional
authorization. But the High Court has not defined the extent to which this independent authority applies
when there has been no sudden attack on the homeland. The executive and legislative branches have
offered differing views on when the President needs Congress’s approval for such military action.
Executive Branch Framework
During the Obama and Trump Administrations, the Department of Justice’s Office of Legal Counsel
(OLC) opined that the Constitution empowers the President to conduct military operations without
congressional authorization under two conditions. First, the President must reasonably determine that the
military action serves “important national interests”—a broad category in which the President possesses a
“great deal of discretion.” Second, the anticipated nature, scope, and duration of the conflict must not rise
to the level of “war” such that it intrudes on Congress’s power to declare war in Article I, Section 8,
Clause 11 of the Constitution. According to OLC, generally only prolonged and substantial military
engagements amount to “war” in the constitutional sense.
Some features of the recent airstrikes in Iraq and Syria are similar to military action that OLC concluded
satisfies its two-prong test for the President to act alone. For example, OLC opined that protecting
American lives and property abroad is a sufficiently important national interest to satisfy the first prong. It
also has opined that some air and missile strikes do not pass the threshold of “war” in the second prong.
At the same time, the current situation presents features that arguably were not present in earlier analyses.
For example, in prong two, OLC examines the risk that an initial strike will escalate into a broader
conflict—a possibility reflected in the President’s public warning concerning Iranian retaliation and
pledge to respond to any such attacks.
Further, OLC has not always been consistent in its legal framework. In 2001, OLC opined that Congress’s
power to declare war does not constrain the President’s “plenary” constitutional authority to use military
force to respond to terrorist threats. OLC expressed a similarly expansive view in a 2002 opinion
concerning Iraq. Although it has rarely cited these opinions, OLC has not withdrawn them as it has other

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opinions related to post-9/11 military action. Reviving this line of reasoning could lead OLC to conclude
that the President possesses broader authority than under its two-prong test.
Congressional Framework
In contrast to OLC, Congress has interpreted the Constitution to create a different legal framework for
evaluating the President’s power to use military force. In Section 2(c) of the War Powers Resolution,
Congress expressed the view that the Constitution permits the President to introduce U.S. forces into
hostilities (or circumstances where hostilities are imminent) only when: (1) Congress has declared war;
(2) Congress has provided specific statutory authorization; or (3) there is a national emergency created by
an attack on the United States or its territories, possessions, or Armed Forces. Courts have not interpreted
the meaning of “national emergency” in the War Powers Resolution, leaving observers to debate whether
such an emergency existed in Iraq and Syria at the time of the recent strikes.
The War Powers Resolution’s analytic framework may require congressional approval to initiate military
action in a broader set of circumstances than what OLC has described. Thus far, however, there has been
no definitive resolution as to which legal framework governs. OLC’s opinions are not binding “law.” At
the same time, the executive branch does not view Congress’s interpretation of the Constitution in the
War Powers Resolution as legally binding. Federal courts, for their part, generally have been unwilling to
resolve the conflict or adjudicate challenges to the President’s authority to initiate military action. Courts
often dismiss such cases on threshold legal grounds without reaching the merits. The ultimate result is
that any congressional disagreement with the President’s claim of constitutional authority may need to be
pursued through political processes rather than in the judicial system. For instance, Congress retains the
power of the purse, which has been effective in limiting the executive branch’s ability to conduct military
operations abroad in some cases.
Did the 2002 AUMF Authorize the President to Conduct the Strikes?
The 2002 AUMF authorizes the President to use the Armed Forces to the extent “he determines to be
necessary and appropriate” to:
1. Defend the national security of the United States against the continuing threat posed by
Iraq; and
2. Enforce all relevant United Nations Security Council resolutions regarding Iraq.
The executive branch relied on the 2002 AUMF as domestic legal authority for the 2003 military
operations in Iraq and deployment of American forces in Iraq in the years that followed (although it also
claimed independent constitutional authority as support for those operations). Since the fall of Saddam
Hussein’s regime, observers have debated whether the authorization to defend against the “continuing
threat posed by Iraq” remains viable. Some argue that the contemplated threat was limited to the dangers
posed by the Hussein regime. Others contend this provision authorizes force for post-Hussein regime
threats emanating from the country of Iraq, regardless of who is in power.
In 2014, the Obama Administration stated it no longer relied on the 2002 AUMF for military action and
supported the statute’s repeal. But later that year the Obama Administration began citing the 2002 AUMF
as domestic authority for its campaign against the Islamic State. Since then, both the Obama and Trump
Administrations have stated that the 2002 AUMF is not limited to threats created by the defunct Hussein
regime. Instead, both Administrations stated that the 2002 AUMF authorizes force for (1) “helping to
establish a stable, democratic Iraq,” and (2) “addressing terrorist threats emanating from Iraq.” Both
Administrations claimed that Congress “ratified” this interpretation by appropriating funds to support
continued military operations in Iraq. In a 2018 report, the Trump Administration stated that the 2002
AUMF “contains no geographic limitation on where authorized force may be employed.”

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During a July 2019 hearing before the Senate Foreign Relations Committee, the Acting Legal Adviser to
the Department of State, Marik String, addressed the Trump Administration’s view of how the 2002
AUMF relates to Iran. He testified that, as of that time, the Trump Administration had not interpreted the
2002 AUMF as authorizing force against Iran except as “may be necessary to defend U.S. or partner
forces as they pursue missions authorized” under the 2002 AUMF. String described the latter exception as
a “nuance” that preserved U.S. and partner forces’ right of self-defense. He elaborated:
where U.S. forces are engaged in operations with partner forces anywhere in the world pursuant to
... [the] 2002 AUMF, if those forces either come under attack or are faced with an imminent armed
attack, U.S. forces are authorized to use appropriate force to respond where it is necessary and
appropriate to defend themselves or our partners.
Based on this description, the Trump Administration appears to interpret the 2002 AUMF to include a
primary authorization for offensive military action for certain purposes and a secondary authorization to
act in self-defense when performing the primary mission. The Trump Administration’s public statements
do not articulate definitively which facet of the 2002 AUMF the President relied upon for the recent
airstrikes. However, the Administration’s emphasis on the defensive purpose of the strike on Soleimani
and Al Muhandis suggests the Administration may argue the secondary authorization applied.
According to String’s testimony, the 2002 AUMF’s secondary authorization arises when U.S. forces are
under attack or faced with an “imminent” attack. As discussed in more detail below, the concept of
imminence often relates to international law and the U.N. Charter. By invoking the imminence
requirement in its interpretation of the 2002 AUMF, however, the Trump Administration may have tied
this heavily debated concept to the President’s claim of domestic authority for the recent airstrikes.
Some Members of Congress have filed lawsuits challenging past Presidents’ conclusions on whether
military conflict was “imminent” in other contexts. But courts have dismissed the suits, reasoning that the
judicial branch was unequipped to resolve the complex factual questions about military threats, and that
the dispute was more appropriately resolved in the political branches. (For discussion of the limits on
congressional participation in litigation and recommendations for what Congress can do in the face of
adverse legal rulings, see this CRS Report.)
Do the Strikes Implicate the Assassination Ban?
Section 2.11 of Executive Order 12333 provides that “[n]o person employed by or acting on behalf of the
United States Government shall engage in, or conspire to engage in, assassination.” President Gerald R.
Ford first put a predecessor assassination ban into place in 1976 after a select committee chaired by
Senator Frank Church (the Church Committee) released a report addressing allegations of possible U.S.
involvement in assassination plots against foreign leaders. While the text of current ban in Executive
Order 12333 appears straightforward, neither it nor earlier executive orders define the term
“assassination.” The lack of clarity has led to longstanding debate over what activities the order prohibits.
A 1989 Department of Army memorandum (known as the Parks Memorandum) separated the legal
framework governing assassinations between peacetime and wartime killings. According to this
memorandum, some peacetime killings for “political purposes” may be considered prohibited
assassinations. During wartime, by contrast, legally sanctioned killing is part of the role of the Armed
Forces, and military forces have much broader legal authority to target and kill enemy forces, the
memorandum posits.
The Parks Memorandum concludes by emphasizing that, regardless of whether it is peacetime or wartime,
Executive Order 12333 does not limit the U.S. forces ability to defend against legitimate threats to
national security. OLC similarly stated in a partially unredacted 2010 opinion that “killings in self-defense
are not assassinations” within the meaning of Executive Order 12333. Accordingly, while the Trump

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Administration did not directly address Executive Order 12333, it may have concluded that the
assassination ban does not apply inasmuch as the recent airstrikes were an act of self-defense.
Finally, in 2016, the Obama Administration stated that using targeted lethal force against an enemy does
not constitute an assassination when it is carried out in manner consistent with the international law
governing the use of force. Consequently, the role of international law (discussed below) may inform
application of the domestic ban on assassination.
What are the Implications under International Law?
The missile strikes against Kata’ib Hizbollah, the Iranian head of IRGC-QF, and the deputy commander
of Iraq’s state affiliated Popular Mobilization Forces may raise questions under international law,
including whether the action is consistent with U.S. obligations under the U.N. Charter. The U.N. Charter
recognizes sovereign equality among Member states, implying an obligation not to interfere in the
domestic matters and territories of one another. Additionally, Article 2(4) of the U.N. Charter prohibits the
“threat or use of force against the territorial integrity or political independence” of another Member state,
or a use of force that is “in any other manner inconsistent with the Purposes of the United Nations,”
unless an exception exists. U.S. forces present in Iraq are operating there pursuant to 2014 requests by the
government of Iraq to the United Nations Security Council seeking international military assistance in the
fight against the Islamic State. Because the recent U.S. airstrikes targeted an Iranian military official but
took place on Iraqi territory, they implicate international legal issues related both to the use of force
against Iran and the territorial integrity of Iraq.
Self-Defense
One exception to Article 2(4) limitations on the use of force is action taken in self-defense. Article 51 of
the Charter explicitly recognizes the right of self-defense as an exception to Article 2(4)’s prohibition.
Specifically, Article 51 states, “Nothing in the present Charter shall impair the inherent right of individual
or collective self-defense if an armed attack occurs against a Member of the United Nations.... ” Some
theorists and practitioners consider that there also exists a customary doctrine of an inherent right to
anticipatory self-defense outside of the circumstances identified by Article 51. This doctrine would permit
military action to counter an imminent grave threat even if no actual armed attack has yet occurred. Under
this view, armed action to counter an imminent threat is not a prohibited “use of force” under Article 2(4)
so long as it is not aimed at taking a state’s territory or subjecting the state’s people to political control,
and is not otherwise inconsistent with the purpose of the U.N. Charter.
An otherwise justified defensive military operation on the territory of another state that does not consent
to the use of force on its territory may violate Article 2(4)’s prohibition against the use of force against
that state. Iraq officials reportedly reacted angrily to the military strikes, and publicly stated that they did
not consent and considered the strikes to be violations of Iraq’s sovereignty and prevailing bilateral
agreements governing the U.S. presence in Iraq. In other instances, the United States has taken the
position that such uses of armed force, arguably like the rocket attacks that took place in Iraq and Syria,
are permissible where the territorial state is “unwilling or unable” to prevent a non-state actor from
carrying out its attacks. To date, U.S. officials have not publicly described Iraq’s government as unwilling
or unable to prevent attacks on U.S. personnel, and President Trump and others have requested that Iraqi
officials continue to uphold their responsibilities to protect U.S. diplomatic facilities.
Imminence
Perspectives differ regarding the meaning of “imminent threat” that would give rise to a right of self-
defense within the meaning of international law. The classic definition of “imminent threat” in this

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context means a threat that is “instant, overwhelming, and leaving no choice of means and no moment for
deliberation.” However, over the last two decades, some U.S. government officials have suggested that a
broader definition taking multiple factors into consideration should apply. For example, former Attorney
General Eric Holder stated that the requirement for imminence, at least in the context of hostilities
involving terrorist organizations, entails “considerations of the relevant window of opportunity to act, the
possible harm that missing the window would cause to civilians, and the likelihood of heading off future
disastrous attacks against the United States.”
Rules Governing Defensive Force
The DOD interprets international law to require self-defensive uses of force to comply with the principles
of necessity and proportionality. To satisfy the necessity requirement, there must be no alternative means
of redress available, and all diplomatic means must either be exhausted or provide no reasonable prospect
of stopping an armed attack. The proportionality requirement involves weighing the contemplated use of
force with the justification for taking action. Self-defense actions are permissible only to the extent that
they are required to repel an armed attack and to restore security. If an actual or imminent attack is part of
an ongoing pattern of attacks, the attacked party may consider what force is reasonably necessary to deter
future armed attacks.
Uses of force taken in self-defense must comply with the rules governing armed conflict, known as
international humanitarian law (IHL) or the law of war, even outside the context of a recognized armed
conflict. Consequently, the armed forces carrying out the defensive actions should minimize the
possibility of civilian casualties and avoid targeting protected objects, including civilian objects not being
used for military purposes or objects whose destruction would likely cause excessive environmental harm.
Cultural sites have additional protection under the Convention for the Protection of Cultural Property in
the Event of Armed Conflict (1954 Hague Convention), which applies “in the event of declared war or of
any other armed conflict which may arise between two or more of the High Contracting Parties, even if
the state of war is not recognized by, one or more of them.” Both the United States and Iran are parties to
the 1954 Hague Convention.
Does International Law Bind the President?
The extent to which such legal constraints on the use of force bind the executive branch is the subject of
an ongoing debate. It is the DOD’s policy to comply with U.S. obligations under the law of war.
However, OLC concluded in a 1989 opinion by then-Assistant Attorney General William Barr that the
President has authority to “override” certain elements of international law, including Article 2(4) of the
U.N. Charter. Although treaties are “supreme law of the Land” under the Constitution, the opinion took
the view that the U.N. Charter is not self-executing (a concept discussed in this CRS Report) and
consequently not binding on the President. Barr wrote that “the decision whether to act consistently with
an unexecuted treaty is a political issue rather than a legal one, and unexecuted treaties, like customary
international law, are not legally binding on the political branches.” Some scholars disagree with that
assessment, however.

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Author Information

Stephen P. Mulligan
Jennifer K. Elsea
Legislative Attorney
Legislative Attorney

Disclaimer
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Congress. Information in a CRS Report should not be relied upon for purposes other than public understanding of
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LSB10391 · VERSION 6 · UPDATED