(Editor’s note: This article was originally published on June 21, 2019. Designed as a expert analysis of the very kinds of questions raised by the U.S. military operation killing Iran’s Qassem Soleimani, we are republishing it today.)

What follows is a basic Q&A on the circumstances under which U.S. military operations against Iran would be lawful under U.S. law. The objective is to provide journalists, lawmakers, and other members of the public a legal framework for this important issue. Our analysis is not specific to any particular scenario — such as Iranian forces’ or so-called Iranian proxies’ attacks on commercial ships, U.S. drones, U.S. military vessels, or U.S. personnel — but rather addresses broader questions about the circumstances under which the president has the authority to initiate U.S. military operations against Iran, whether Congress has already authorized the use of force against Iran, how the War Powers Resolution fits into the picture, and what Congress can do if it disagrees with the president’s course of action.

1. Does the president need authorization from Congress to use U.S. military force against Iran?

The president derives authority to use military force overseas from two sources: the Constitution and congressional authorization. At this point, we do not believe that there is any existing congressional authorization to use force against Iran (see Q2 below). In the absence of congressional authorization, the president could only use force against Iran by relying on his authority over foreign relations and as commander-in-chief under Article II of the Constitution.

There is considerable debate on the scope of the president’s authority to use military force in the absence of congressional authorization. The executive branch, through consistent historical practice in Republican and Democratic administrations, and as reflected in a series of opinions by the Justice Department’s Office of Legal Counsel (OLC), has taken a relatively broad view of the president’s Article II authority to initiate the use of force, arguing that it has the ability to do so when: (1) there is an important “national interest” in doing so (Curtis Bradley and Jack Goldsmith have explained that this has become a very expansive concept in modern practice; Marty Lederman has suggested the concept should be understood as limited to significant national interests that have historically supported such unilateral actions in the past); and (2) the use of force does not constitute “war” in the constitutional sense.

The latter limitation is because Article I of the Constitution delegates the power to “declare war” to Congress. The executive branch has argued, in essence, that if the expected “nature, scope, and duration” of the military engagement falls below the threshold of “war,” the president may use force without congressional authorization. In the OLC’s view, “military operations will likely rise to the level of a war only when characterized by ‘prolonged and substantial military engagements, typically involving exposure of U.S. military personnel to significant risk over a substantial period.’” The OLC opined most recently that the limited strikes against Syria by the United States in response to Syrian President Bashar al-Assad’s use of chemical weapons did not cross this threshold. Prior OLC opinions reached a similar conclusion with respect to U.S. military strikes in Libya in 2011, and U.S. military activities in Haiti in the 1990s, among others.

In the War Powers Resolution of 1973 (WPR), Congress imposed important limitations on the president’s ability to conduct military operations in the absence of explicit congressional authorization. Indeed, Congress does not necessarily view its own authority so narrowly or the president’s so expansively as described in the OLC opinions noted above. The WPR explicitly states the view of Congress that the president’s constitutional authority to introduce U.S. Armed Forces into hostilities, or situations where involvement in hostilities is imminent, may be exercised “only pursuant to (1) a declaration of war, (2) specific statutory authorization, or (3) a national emergency created by an attack upon the United States, its territories or possessions, or its armed forces.” Moreover, as explained below, the WPR requires the relevant military operations (“hostilities”) to be terminated after a defined period of time unless they have been authorized by Congress.

The framers of the Constitution gave the authority to declare war to Congress, as well as the authority to raise and support armies, provide and maintain a Navy, provide for the common defense, regulate detention and seizure of vessels in war, and a host of other powers related to war and foreign affairs, in part to prevent the United States from being drawn into conflict for unpopular purposes or without debate and consideration by the representatives of the people. The Constitution’s design anticipates that Congress would be less inclined to go to war than the executive branch — this is a feature, not a bug. (Of note, it has long been understood that even though Congress has the lion’s share of authority in war-making, the president does have at least some concurrent if not exclusive authority in regard to the conduct of hostilities and to use force to repel a sudden attack on the United States.)

What’s more, even in the OLC’s view, the threshold for “war” in the constitutional sense is more easily met when the use of force at issue is against against another nation state (rather than in its territory but with its consent) where there is a high likelihood of escalation. Although Iran is not a nuclear power, which would necessarily affect that calculus, its capacity as a nation-state with a strong military, including its cyber and ballistic missile capabilities, are relevant factors in this analysis, as is the extent of U.S. exposure given its significant footprint in the region where Iranian military forces (and their proxies) are present and active. The scope of U.S. objectives for the use of force will also affect the analysis, especially if those objectives are likely to require sustained operations or engender use of force in response by Iran. Those factors may distinguish this case from the U.S. strikes against Syria, for example.

Finally, another important limitation is that the president’s use of force — whether based on congressional authorization or not — must comply with international law. The president is charged in Article II of the Constitution to “take care” that the laws are faithfully executed. This includes our international legal obligations, including the U.N. Charter, which prohibits the threat or use of force except in certain limited circumstances, such as self-defense. Also, under international law, even if the United States acts in self-defense, the U.S. response must be necessary and proportionate.

2. Does the president have authorization from Congress to strike Iran? Specifically, would the 2001 Authorization for the Use of Military Force (AUMF) authorize a strike against Iran?

There is no existing congressional authorization for the use of force against Iran. While some in the Trump administration, including Secretary of State Mike Pompeo, have made arguments attempting to link Iran and al-Qaeda — in what may be an effort to lay the groundwork for invoking the 2001 AUMF, which was passed in the aftermath of the 9/11 attacks, as authorization to use force against Iran — that argument is thoroughly unconvincing.

The 2001 AUMF authorizes the president to use:

“necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001, or harbored such organizations or persons, in order to prevent any future acts of international terrorism against the United States by such nations, organizations or persons.”

This has long been understood to refer to al-Qaeda and the Taliban, who harbored al-Qaeda in Afghanistan at the time of the 9/11 attacks, and also has been interpreted by all three branches of government to apply to “associated forces” of those two armed groups based on the principle of co-belligerency in armed conflict.

As we have previously written: “The 2001 AUMF does not authorize the use of force against Iran. Iran was not implicated in the 9/11 attacks, Iranian forces are not al Qaeda or the Taliban, or their associated forces, nor are they a ‘successor’ to any of those forces.”

Many have suggested that Pompeo and other officials may be laying the groundwork for an argument that the 2001 AUMF authorizes military operations against Iran because Iran is “harboring” some members of al-Qaeda. As a factual matter, we are not aware of any credible information that Iran is “harboring” al-Qaeda as a group, or allowing al-Qaeda to plot attacks from Iran. As a legal matter, the AUMF has never been construed to authorize military attacks against a foreign nation based on the fact that some al Qaeda members may be located in or transit that country, even if that is the case with Iran. In addition, the AUMF’s use of the past tense — “harbored” — suggests that it was intended to refer to those who were responsible for providing safe haven for, and otherwise assisting, those who attacked the United States on Sept. 11, 2001. In the 20 years since the 9/11 attacks, there has not been any suggestion that the 2001 AUMF could be interpreted to authorize force against a present-day “harborer.” (Again, there is no known evidence to suggest that is what Iran is doing with al-Qaeda.)

The 2001 AUMF authorizes force only if it is consistent with international law, as the Supreme Court explained in Hamdi v. Rumsfeld. Even if the 2001 AUMF were somehow thought to apply to Iran — which it does not — the executive branch would be able to use force against Iran only if necessary and proportionate to the specific threat from al-Qaeda.

In a House Foreign Affairs Committee hearing on June 19, Rep. Deutch (D-Fl.) asked State Department Special Representative for Iran, Brian Hook, whether he believes “the administration could launch an attack against Iran under the 2001 AUMF?” His response, “this is something which the office of the Legal Adviser can give you an opinion on, if you’d like to submit it,” provides an appropriate next step for Congress to engage with the administration on this issue.

Finally, it bears noting that there is no viable argument that another AUMF still on the books — the “Authorization for Use of Military Force Against Iraq Resolution of 2002” (2002 AUMF) — authorizes force against Iran. It allows the president to use force that is “necessary and appropriate” to “defend the national security of the United States against the continuing threat posed by Iraq;” and “enforce all relevant United Nations Security Council resolutions against Iraq.” Those are plainly not relevant to the situation with Iran today.

3. What steps can Congress take if it disagrees with the president’s decision to use military force? More specifically, what steps can Congress take in advance to prevent actions by the president? And, what steps would Congress be able to take after the president uses force against Iran if lawmakers are opposed?

Congress has a number of tools at its disposal to constrain the president’s ability to use force unilaterally. Even in the OLC’s view, the president’s ability to use force without congressional authority can be checked if Congress decides to impose restrictions. While past attorneys general and the OLC have determined the president has the power to use military force abroad to protect important national interests and below the threshold of “war” in the constitutional sense, as discussed above, “[t]his independent authority of the President … exists at least insofar as Congress has not specifically restricted it,” the OLC wrote in 2011.

Congress’ appropriations power is one of the most potent tools to restrict presidential action. In 2018, the OLC opined that the significant powers vested in Congress by the Constitution “ensure that the use of force ‘cannot be sustained over time without the acquiescence, indeed the approval, of Congress, for it is Congress that must appropriate the money to fight a war or a police action.’ … These powers further oblige the President to seek congressional approval prior to contemplating military action that would bring the Nation into a war.”

Notably, an amendment to the National Defense Authorization Act for Fiscal Year 2020 (FY20 NDAA), which was debated last week in the House Armed Services Committee, would have prohibited the use of federal funds to use military force in or against Iran absent Congress declaring war or enacting specific statutory authorization, with the exception of a “national emergency … created by an attack upon the United States, its territories or possessions, or its armed forces.”

While the amendment was withdrawn after lengthy discussion, Rep. Adam Smith, the Democratic chairman of the committee, has committed to “a vote on a similar proposal when the FY20 NDAA comes to the floor of the House of Representatives.” (The amendment was offered by Reps. Ro Khanna (D-Calif.), Anthony Brown (D-Md.), John Garamendi (D-Calif.), and Seth Moulton (D-Mass.).

It is precisely this type of action — the cutting off of funds for specific uses of force, which relies on Congress’ constitutional appropriations power — that would put Congress on its strongest footing to assert authority over the use of force abroad, and would put the president’s authority at what the Supreme Court has described as its “lowest ebb.” The clear intent of this proposed amendment is to prevent the executive branch from drawing the United States into a war without a congressional vote to specifically authorize it, which is particularly important given that senior Trump administration officials are considering justifying a use of force against Iran on purported congressional authorization in the 2001 AUMF.

Finally, an amendment like this could be passed even after an initial use of force, making clear the president does not have authority to continue using force absent congressional authorization.

4. Does the War Powers Resolution authorize the president to use force? What does the War Powers Resolution require the president to do before taking military action? What does it allow Congress to do after the president uses force abroad without authorization?

The War Powers Resolution (WPR) does not authorize the president to use force. It is a common misperception to think otherwise. The law’s stated purpose is “to fulfill the intent of the framers of the Constitution… and insure that the collective judgment of both the Congress and the President will apply to the introduction of United States Armed Forces into hostilities, or into situations where imminent involvement in hostilities is clearly indicated by the circumstances…” And as noted above, it takes a limited view of the president’s authority to introduce U.S. Armed Forces into such situations in the absence of congressional authorization or an attack on the United States.

Before the president involves U.S. forces in hostilities abroad (or circumstances where hostilities are likely), the WPR requires the president to “consult with Congress.” The WPR also requires the president to report to Congress within 48 hours whenever certain conditions are met that could lead to the United States getting drawn into a war that Congress hasn’t authorized. Those conditions are when U.S. Armed Forces are introduced: (1) into hostilities (or where involvement in hostilities is “clearly indicated by the circumstances”); (2) into the territory, airspace, or waters of a foreign nation while equipped for combat (except for routine deployments for “supply, replacement, repair, or training” of U.S. forces); or (3) in “numbers which substantially enlarge” U.S. forces equipped for combat already in a foreign nation.  

Finally, the heart of the WPR is its termination provision, which is intended to provide a mechanism to ensure the president does not continue to involve U.S. forces in hostilities without specific congressional authorization. Under the WPR, the president must “terminate any use” of U.S. Armed Forces that were introduced into hostilities (or where involvement in hostilities is clearly indicated by the circumstances) 60 days after the required notification unless Congress has specifically authorized that use of U.S. Armed Forces by statute, passed a law extending the 60-day period, or has been “physically unable to meet as a result of an armed attack upon the United States.” 

The Executive Branch has not adopted a consistent view on the constitutionality of the WPR’s termination provision.  President Nixon’s veto statement concluded that much of the WPR, including the 60-day clock, was unconstitutional, and OLC made a passing suggestion to the same effect in John Yoo’s subsequently repudiated 2001 memo on the AUMF. On the other hand, OLC concluded in 1980 that Congress may “as a general constitutional matter” place time limits on the use of armed forces without express Congressional authorization, and this position was reaffirmed by the Obama Administration.

There is significant debate, to say the least, regarding what constitutes “hostilities” for the purposes of the War Powers Resolution. Both the Obama and Trump administrations, for example, took the position that providing aerial refueling and intelligence support to the Saudi-led coalition in the conflict in Yemen did not constitute introducing U.S. forces into “hostilities.” Moreover, recent experience has shown that unless Congress has sufficient votes to override a presidential veto of a resolution requiring termination of the use of U.S. Armed Forces, it may be unable to stop military engagement abroad once it has begun using the mechanism of the WPR alone, so long as the president believes that the military engagement in question does not constitute “hostilities.”

This is all the more reason why cutting off funds for the use of military force against Iran, in the absence of congressional authorization or an armed attack by Iran on the United States or its armed forces, would be a more effective tool to curtail the ability of the executive branch to draw the United States into a war that Congress has not authorized.

[Editor’s Note: Just Security will soon publish a similar analysis on the international law questions concerning military actions between the United States and Iran. Stay tuned.]

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