On June 21, 2025, the United States joined the Israel-Iran conflict by conducting airstrikes on three Iranian nuclear facilities—Operation Midnight Hammer. This attack—involving B-2 stealth bombers flown from Whiteman Air Force Base in Missouri—was the first ever direct U.S. military attack against Iranian territory and the first use of the GBU-57, a 30,000 pound bunker busting munition, in combat. (The Carter administration of course conducted Operation Eagle Claw, but that was a rescue mission.) And it was conducted without congressional authorization.
On June 23, the White House sent to Congress a notification under the War Powers Resolution of 1973 articulating both domestic and international legal arguments justifying the attack on Iran. These justifications are unconvincing, raise profound concerns as to whether the Executive Branch has adopted expansive new legal theories justifying the use of force, and now should provide additional impetus for Congress to push back against this unauthorized attack on Iran.
Constitutional Framework: Article I v. Article II
Article I of the U.S. Constitution assigns the power to “Declare War,” and related authorities to the Congress. The framers of the Constitution intended collective decision making to slow recourse to war and to help ensure proper deliberation over consequential decisions involving U.S. blood and treasure.
Congress exercises this prerogative through declarations of war (such as those it made against the Axis powers in World War II) as well as statutory authorizations of the use of military force (such as those for post-9/11 counter-terrorism military operations and the 2003 Iraq war).
By contrast, the president’s unilateral war powers principally flow from his or her status as “commander-in-chief” under Article II of the constitution.
The constitution’s framers clearly intended the division of war powers between Congress and the president to serve as a conflict prevention mechanism. They believed that the president should have unilateral authority to repel “sudden attack” – but beyond that they envisioned that assigning to the people’s representatives in the legislature the power to declare war would be a brake on imprudent war-making. They anticipated that Congress, as a deliberative body and facing collective action challenges, would be less prone to rush into war than a single person – the president – might be if he or she had sole discretion.
Although the exact division of war powers between Congress and the president has long been subject to debate, as a practical matter the president’s powers have expanded over time. Particularly since the Second World War, the executive branch has taken an increasingly capacious view of the president’s authority to direct the use of force under Article II of the Constitution as commander in chief in the absence of congressional authorization. The executive branch legal doctrine for the president’s authority to use force unilaterally is articulated in a series of legal opinions issued by the Department of Justice’s Office of Legal Counsel (OLC) which acts as something of an internal Supreme Court within the executive branch. According to the dominant OLC framework, whether the president may unilaterally use force depends on a two-part test.
(1) Whether the U.S. military operations would serve sufficiently important national interests; and
(2) Whether the military operations that the president anticipates ordering would be sufficiently extensive in “nature, scope, and duration” to constitute a “war” within the meaning of Article I, § 8, cl. 11, which gives the Congress the power “[t]o declare War.”
As concerns the “national interest” test, first and foremost amongst these is defense of the United States, but over time OLC has identified others as well – from support of the United Nations to mitigating humanitarian disasters. OLC has framed whether a national interest would justify the use of military force as one where the “President reasonably determined the operation would further important national interests.” In practice, as Jack Goldsmith, a former head of OLC, and Curt Bradley have noted, the “national interest” test has been applied so broadly by DOJ that it is essentially meaningless as a constraint on executive power. Therefore, to the extent that executive branch war powers doctrine constrains the unilateral use of force by the president under domestic law, it is likely to be the second element regarding “war in the constitutional sense” that is load bearing.
In evaluating whether a proposed military action would amount to such a “war,” and thus require congressional authorization, OLC has looked to the anticipated “nature, scope, and duration” of the operation. Under this framework, military operations will likely rise to the level of war if they are anticipated to be characterized by “prolonged and substantial military engagements, typically involving exposure of U.S. military personnel to significant risk over a substantial period.”
OLC has identified one particularly salient factor in reviewing whether an anticipated military operation amounts to this level of “war in the constitutional sense”: the risk of escalation.
In assessing the risk of escalation, OLC has considered whether U.S. forces would suffer or inflict substantial casualties and thus has looked closely at the presence of ground troops given “the difficulties of disengaging ground forces from situations of conflict, and the attendant risk that hostilities will escalate.” In analyzing the proposed deployment of U.S. forces to Bosnia in 1995, for example, OLC observed that due to the presence of U.S. ground forces in a conflict, “Congress may be confronted with circumstances in which the exercise of its power to declare war is effectively foreclosed.” Crucially, when OLC considered the deployment of U.S. ground troops in Bosnia in 1995 and pronounced it not amounting to “war,” it was in the context of U.S. forces seeking to ensure compliance with a peace agreement. That of course is a very different scenario than U.S. ground forces being deployed to a region and the United States starting an armed conflict, subjecting those troops to potential retaliation.
It is important to emphasize that this OLC two-part test is an executive branch doctrine which has been neither adopted nor endorsed by either Congress or the courts.
Statutory Framework: War Powers Resolution
Aside from the constitutional conditions, the statutory framework intended to govern the unilateral use of force by the president, such as the recent strikes in Iran, is the War Powers Resolution. Congress enacted this law over President Richard Nixon’s veto in 1973 to reassert its constitutional prerogatives with respect to war and peace in the final stages of the Vietnam War. Specifically, Congress sought to forestall any president from sliding the country into war without congressional authorization or even without congressional awareness (as had allegedly been the case for aspects of the war in southeast Asia, such as Nixon’s secret incursion into Cambodia in 1969).
To this end, Section 4(a) of the Resolution establishes reporting requirements to prevent the president from taking the country to war in secret. In the absence of a congressional declaration of war or other statutory authorization, the president is subject to multi-tiered obligations to report on certain triggering activities of U.S. armed forces within 48 hours to Congress.
First, under subsection 4(a)(1) he or she must report when U.S. military forces are introduced into “hostilities” or introduced into “situations where imminent involvement in hostilities is clearly indicated by the circumstances.” Such hostilities reports are the focus of this essay.
Second, even if U.S. forces are not engaging in hostilities, subsection 4(a)(2) requires the president to report the introduction of “combat equipped” forces into a country (the executive branch defines “combat-equipped” as forces equipped with crew-served weapons such as machine guns requiring more than one person to operate and mortars).
Third, pursuant to subsection 4(a)(3), the president must also report a substantial enlargement of such combat equipped forces in a country where such forces are already present.
Notably, under Section 5(b) of the 1973 Resolution, the submission of a report under the first of these scenarios — introduction of U.S. forces into hostilities or situations of imminent hostilities — also starts a 60-day clock for the withdrawal of U.S. armed forces from such hostilities unless Congress declares war or otherwise enacts specific statutory authorization for the use of force. Further, the War Powers Resolution provided a mechanism in section 5(c) for Congress to order the removal of U.S. forces from hostilities through a concurrent resolution—that is, a resolution passed by both houses of Congress but not presented to the president for his or her signature or veto. Particularly following the Supreme Court’s 1983 decision in INS v. Chadha that ruled unconstitutional the legislative veto, section 5(c) is widely viewed as unconstitutional. In the wake of Chadha Congress enacted expedited procedures for joint resolutions in the Senate (but not the House) requiring the removal of U.S. armed forces from hostilities, which does require presentment to the president for a signature or veto.
Although Congress did not define “hostilities,” or “imminent involvement in hostilities,” in the text of the statute, the legislative history indicates that Congress intended those terms to be construed broadly in order to establish a low threshold for both the reporting and withdrawal provisions of the War Powers Resolution. The House Foreign Affairs Committee’s report on the Resolution explains:
The word hostilities was substituted for the phrase armed conflict during the subcommittee drafting process because it was considered to be somewhat broader in scope. In addition to a situation in which fighting actually has begun, hostilities also encompasses a state of confrontation in which no shots have been fired but where there is a clear and present danger of armed conflict. “Imminent hostilities” denotes a situation in which there is a clear potential either for such a state of confrontation or for actual armed conflict. (emphasis added)
One significant mechanism for weakening the constraints imposed by the War Powers Resolution has been the executive branch’s permissive interpretation of key terms left undefined in that text. Some of these are crucial to determining when the resolution’s reporting and withdrawal requirements are triggered. For example, the State Department’s Legal Adviser informed Congress in a 1975 letter that its working definition of “hostilities” meant “a situation in which units of the U.S. armed forces are actively engaged in exchanges of fire with opposing units of hostile forces.” “Imminent hostilities” means “a situation in which there is a serious risk from hostile fire to the safety of United States forces.”
Based on the legislative history, lawmakers had in mind a much broader definition – one that would encompass confrontations before shots are fired. Further, as a matter of statutory interpretation, it is questionable how much weight the post-enactment views of the executive branch should be accorded as opposed to the pre-enactment interpretation of the legislature that passed the statute into law over the president’s veto.
Nonetheless, the State Department’s 1975 approach to hostilities has nonetheless generally prevailed for five decades. The president has thus had significant latitude to deploy troops into potentially hostile situations without setting off the 60-day clock to withdraw forces.
Executive branch lawyers have also interpreted what it means to “introduce” armed forces into hostilities – another concept that bears on when the 60-day clock starts ticking. In a 1980 opinion, OLC took the position that:
if our armed forces otherwise lawfully stationed in a foreign country were fired upon and defended themselves, we doubt that such engagement in hostilities would be covered by the consultation and reporting provisions of the War Powers Resolution. The structure and thrust of those provisions is the “introduction” of our armed forces into such a situation and not the fact that those forces may be engaged in hostilities. It seems fair to read “introduction” to require an active decision to place forces in a hostile situation rather than their simply acting in self-defense.
Recently, the Biden administration relied on such narrow interpretations of “introduction into hostilities” to avoid starting the Resolution’s 60-day clock both with respect to hostilities with the Houthis and U.S. missile defense of Israel from Iranian fusillades in April and October 2024. The Trump administration also appears to be relying on the theory that shooting down Iranian drones and missiles aimed at Israel does not constitute an introduction into hostilities because U.S. forces are not firing at Iranian forces, but instead at unmanned systems.
Contrary to some misunderstandings, the War Powers Resolution does not provide affirmative authority to use force. Nor does the Resolution itself categorically prohibit the unilateral use of force by the President. Instead, it imposes notification requirements, time limits for qualifying military actions, and expedited mechanisms for congressional response to unilateral action by the executive.
International Law
As with the US Constitution, U.S. treaty obligations also impose legal limits on the use of force and ought to pose a significant hurdle to U.S. attacks on Iran. Article 2(4) of the U.N. Charter prohibits “the threat or use of force against the territorial integrity or political independence of any State, or in any other manner inconsistent with the Purposes of the United Nations.” Article 51 of the Charter also provides that the treaty does not “impair the inherent right of individual or collective self-defence” in the event of an armed attack.
As I have previously argued, this prohibition on the use or threat of force is not only binding on the United States under international law, it imposes domestic legal obligations on the president individually, as the president has a constitutional duty to “take Care that the Laws be faithfully executed” and the “Laws” encompass treaties, specifically including the UN Charter.
The June 23 War Powers Report
There are several notable legal aspects of the Trump administration’s letter to Congress regarding the attack on Iran.
First, the administration cites the President’s authority as Commander in Chief and Chief Executive and his “constitutional authority to conduct United States foreign policy” under Article II of the Constitution as the sole domestic legal basis for the attack. The administration does not invoke either the 2001 Authorization for the Use of Military (2001 AUMF) or the Authorization for Use of Military Force Against Iraq Resolution of 2002 (2002 Iraq AUMF) as supposed authority for the U.S. strikes.
Reliance solely upon the President’s supposed authority under Article II for the strikes is notable given some of the legal arguments of the prior Trump administration. Under Trump 1.0, his Secretary of State had begun laying the groundwork for suggesting the 2001 AUMF—which was targeted at those responsible for the 9/11 attacks and provides the statutory basis for the war on terror—also applied to Iran. Further, in justifying the 2020 strikes on Iranian General Qassem Soleimani in Baghdad, Iraq, the first Trump administration invoked the 2002 Iraq AUMF alongside Article II as domestic legal authority. Yet, according to congressional staff I spoke with, the first Trump administration had conceded that this Iraq war authorization would not cover an attack on Iranian territory. Perhaps this understanding of the limits of the 2002 Iraq AUMF has persisted.
Second, evoking the OLC framework, the report states that the “strikes were taken to advance [unspecified] vital United States national interests.” The White House also takes pains to emphasize the supposed absence of factors militating toward the attack amounting to “war,” which would require congressional authorization under the OLC scheme.
The strike was limited in scope and purpose. The United States discretely targeted three Iranian nuclear facilities. Iranian troops and other military facilities were not targeted. No United States ground forces were used in the strike, and the mission was planned and executed in a manner designed to minimize casualties, deter future attacks, and limit the risk of escalation.
Third, the White House letter to Congress also claims that the attack on Iran was “necessary and proportionate action consistent with international law.” The apparent international legal justification—referenced elsewhere in the letter—is the “collective self-defense of our ally, Israel.”
Problems with the Trump Administration’s Legal Arguments
There are a number of flaws with the legal justifications advanced by White House.
First, the Trump administration does not clearly identify the supposed “vital United States national interests” justifying the attack on Iran. That includes what exactly the U.S. intelligence community or Trump considered to be the threat from Iran’s nuclear program at this time. Given reporting on the decision making leading up to the attack—including the role television coverage may have played in it—there are questions about whether the president did in fact “reasonably determine” that the attacks advanced U.S. national interests. More fundamentally, given the time period during which his administration was deliberating over the potential use of military force against Iran, there was ample time for the White House to consult with and seek authorization from the U.S. Congress—as the administration of George W. Bush did prior to attacking Iraq over its purported weapons of mass destruction.
Second, in seeking to minimize the nature of the military operation to avoid the limit of “war in the constitutional sense” the administration neglects to mention that while no ground forces were used in the attack, tens of thousands of U.S. troops are stationed within missile range of Iran—predictable targets for Iranian retaliation – which Iran of course carried out, in part, on June 23, though reportedly after first sending private warning so as to avoid or at least minimize casualties. There’s good reason to think Iran will retaliate later with covert means.
Certainly, at this point, we should hope that there is in fact no further escalation and that the parties to this conflict somehow find a way to return to diplomacy to resolve remaining differences. That said, the question that lawyers should have been asking prior to the strikes were about risks, not hopes. Here, it is hard to imagine a credible risk analysis that would fail to account for Iran’s size, sophisticated kinetic and cyber weaponry, proximity to U.S. troops deployed throughout the region and history of using covert and asymmetric tactics to gain revenge over time. Indeed OLC doctrine expressly states that some of these factors risks of substantial casualties to U.S. forces and “the difficulties of disengaging ground forces from situations of conflict, and the attendant risk that hostilities will escalate” should figure into an assessment of whether operations constitute “war in the constitutional sense.” Thus, although the administration’s 48-hour report intones the right formulas to meet the OLC standard, the factual picture they present does not suggest they reached their conclusions by way of rigorous legal and factual analysis.
Third, the international legal justification for the U.S. attack on Iran—collective self-defense of Israel—appears to rest on the underlying lawfulness of Israel’s own use of force against Iran. The emerging consensus amongst international lawyers is that Israel’s attack on Iran was in fact unlawful (see here and here, but see here). As Marko Milanovic notes, “were this issue to come before the International Court of Justice, say in advisory proceedings, a great majority of the Court’s judges (maybe even 14 to 1…) would say that Israel has used force unlawfully.” Reporting that the Israeli government had decided to attack Iran last year undercuts the notion that the use of force was necessary—that is there was no choice of means—and that Israel’s attack was in response to an imminent threat. Instead, it seems a war of choice.
Indeed, in 1981, the United States joined a unanimous UN Security Council resolution in condemning a very similar preventative Israeli attack on the Iraqi nuclear facility at Osirak. The United States opined that Israel’s actions violated Article 2(4) due to the “absence of any evidence that Iraq had launched or was planning to launch an attack that could justify Israel’s use of force. … [T]he presence in a State of the military capacity to injure or even to destroy another State cannot itself be considered a sufficient basis for the defensive use of force.”
As Israel’s attack on Osirak relied on U.S. warplanes, it implicated the requirement imposed by the Arms Export Control Act that U.S.-supplied weapons be used in “legitimate self-defense,” which includes compliance with Article 2(4) of the UN Charter. As a result, the Reagan administration temporarily paused further deliver of subsequent warplanes. Because Israel’s attack on Iran also involves U.S.-origin warplanes, the application of the Arms Export Control Act is once again relevant.
If the United States has now endorsed Israel’s theory of preventative self-defense, that would represent a dramatic shift in U.S. legal views with potentially profound and destabilizing implications. (Despite some misunderstanding to the contrary, the United States did not rely on preventative self-defense as the international law justification for the 2003 invasion of Iraq, but instead claimed authority to invade Iraq on the basis that Iraq materially breached a Security Council ceasefire resolution.) Such an expansive (and unsupported) understanding of self-defense would greatly expand the scope for potential uses of force. (The fact that the Trump administration submitted this legal notification consistent with the War Powers Resolution suggests that they may submit a further notification to the UN Security Council under Article 51 of the Charter. Such an Article 51 letter may elaborate further on the administration’s international legal theory.)
Congress’s Turn
Even prior to the White House articulating its legal theories supposedly justifying the attack on Iran, some members of Congress had denounced the strikes as illegal and unconstitutional. At least four pieces of legislation have been introduced to push back on the Trump administration’s unsanctioned attack.
In the Senate, Tim Kaine (D-VA) has introduced a joint resolution under the War Powers Resolution requiring the President to “terminate the use of U.S. Armed Forces for hostilities” against Iran. This joint resolution is modelled on legislation that Senator Kaine introduced in 2020 following Trump’s previous killing of Iranian General Qassem Soleimani. That resolution passed both houses of Congress with bipartisan support but was vetoed by President Trump. It remains an important precedent for the maintenance of Congress’ views on the law and its institutional prerogatives. Should Kaine’s 2025 joint resolution pass both houses, Trump would almost surely veto it as well.
In the House, Representatives Tom Massie (R-KY) and Ro Khanna (D-CA) have introduced a concurrent resolution. The draft resolution “directs the President to terminate the use of United States Armed Forces from hostilities against” Iran. Yesterday, the ranking members of the House Foreign Affairs, Armed Services, and Intelligence committees introduced a second concurrent resolution, to require the removal of U.S. armed forces from hostilities with Iran.
In the Senate, there are expedited procedures for joint resolutions under the War Powers Resolution—which would have the force of law if enacted and either signed by the president or passed over this veto. However, such expedited procedures are absent in the House. Instead, the expedited procedures in the House pertain only to concurrent resolutions which would not be presented for the president’s signature. Following the Supreme Court’s decision in Chadha, such concurrent resolutions are generally regarded as lacking the force of law.
Should either the Senate or House resolution gain traction, it would send a signal of congressional frustration with Trump’s war-making initiative. Such signaling carries weight and can send an important message to U.S. security partners—as was the case with a 2019 joint resolution relating to U.S. support for the Saudi-led military campaign in Yemen. That said, as a legal matter, there are limits to how effective a resolution that is not passed into law can be. Moreover, because of the interpretive holes in the War Powers Resolution, even if the House or Senate measures were to be enacted, the Trump administration might claim that U.S. troops are no longer engaged in hostilities (or never were) so there is nothing for them to terminate. Thus the barriers to enforcement are quite high.
Congress does have stronger medicine at its disposal, however. Senator Bernie Sanders (I-VT) has introduced legislation barring funding for any use of military force against Iran except if authorized by Congress. Such legislation seeks to deploy what some have dubbed the “ultimate war power”—the power of the purse. Indeed, such funding prohibitions are how Congress ultimately terminated U.S. involvement in the Vietnam War.
Of these measures, Kaine’s resolution appears on course to receive a procedural vote soon—possibly as early as this week. When or whether the other measures will receive votes is less clear.
The significance of all these measures—particularly the Kaine joint resolution—lies not in its likelihood of becoming law but in sending a political signal to the White House about congressional opposition to its unilateral military action. The greater the support and more bipartisan that support is, the stronger that signal. Even if the ceasefire that Trump announced yesterday comes into effect, such congressional efforts will provide an important backstop to the United States reentering and further fighting between Israel and Iran.
In addition, members of Congress who wish to uphold the legal architecture governing the use of force can and should continue to make their own legal views known both with respect to the domestic and international legal justifications offered by the Trump administration for attacking Iran. These congressional legal positions can be articulated singly by members including during floor debates or collectively through amendments to these legislative measures, free-standing resolutions, or letters to the administration. It is important for this and future presidencies that the Trump administration’s flawed and dangerous legal justifications not be the last U.S. government word on the lawfulness of attacking Iran or the parameters of domestic and international law.
