How Legal Authorization for Military Force Escalated Under Trump

The March 28, 2025 letter to Congress did not try to do very much, which is precisely why it matters. It reported that U.S. forces had begun strikes against Houthi targets in Yemen on March 15, after attacks and threats against U.S. naval vessels and commercial shipping, and it located the President’s authority in Article II as Commander in Chief and Chief Executive. It did not identify a statute authorizing force. It did not invoke a United Nations Security Council mandate. It presented the operation as a self-defense measure tied to a particular set of Houthi attacks on U.S. forces and maritime traffic.[1][2]

That narrowness gave the notice its legal shape. The problem was not only the use of force; it was the way the first claim entered the record. The letter came 13 days after strikes began, a delay that Lawfare flagged in its discussion of the War Powers Resolution notice requirement.[2] If the administration’s position had stopped there, the legal file would still have raised hard questions about Article II, Yemen, and the Houthis. But it would have remained a relatively bounded self-defense claim: U.S. ships were attacked or threatened; U.S. forces struck Houthi targets; Congress was notified after the fact.

The later difficulty is that the bounded claim did not stay bounded. Across the next operations, the administration’s legal theory moved from direct self-defense against Houthi attacks, to collective self-defense of Israel in a limited strike on Iran’s nuclear capacity, and then to a theory that the United States was already in an ongoing international armed conflict with Iran. The target changed, the scope widened, and the temporal limit became less visible.

The First Constraint Was the Target

The March 2025 Houthi letter still did one important limiting thing: it tied force to the group whose conduct supplied the asserted defensive predicate. That matters under both domestic and international-law analysis. Article II practice has often tolerated some unilateral uses of force, but the legal risk changes when an executive branch claim migrates from the actor that attacked U.S. forces to another state said to be connected to that actor.

The administration’s later posture depended on doctrines that can perform that migration. One is the “accumulation of events” theory, under which repeated incidents may be treated together rather than as isolated episodes. Another is attribution through “substantial involvement,” a contested standard associated with debates over when a state’s support for armed groups can justify self-defense against the state itself. The International Court of Justice’s Nicaragua analysis is part of the background here, and later scholarship on U.S. and U.K. strikes in Yemen underscores how disputed these theories remain in the jus ad bellum setting.[3][4]

Those doctrines are not decorative. They are the legal joints that let an operation initially described around Houthi conduct support a broader account of Iranian responsibility. A reader looking only for the battlefield sequence will miss the point. The relevant change is not simply that Iran appears later in the story; it is that the legal record needed a way to make Iran more than a background patron without a fresh congressional authorization.

For readers focused on the separate blockade question, the narrower international-law issue is treated in more detail in Does the Houthi Blockade Trigger Self-Defense Rights Under International Law?.

Midnight Hammer Preserved a Limit the Next Memo Would Need to Escape

Operation Midnight Hammer, in June 2025, moved the legal center from Houthi attacks on U.S. forces to collective self-defense of Israel. The administration’s asserted object, as reflected in the research record, was limited: a nuclear-disabling operation against Iran. That shift loosened the target constraint. Iran was no longer treated merely as a supporting state behind Houthi attacks; it became the object of U.S. force.

But Midnight Hammer still had an apparent limiting feature. It was not initially framed as an open-ended war with Iran. A limited collective-defense theory asks different questions from an ongoing-conflict theory: what armed attack triggered the response, whose defense is being invoked, which targets are necessary to repel or prevent the attack, and when the defensive episode ends. Those are constraint questions, not academic embellishments.

The administration’s later legal problem was temporal. The research record includes Trump’s own declaration that the June 2025 conflict was at an “Official END.” That statement matters less as rhetoric than as a record marker. If the conflict ended, then a later operation needs either a new armed-attack predicate, a new statutory authorization, or a persuasive explanation for why “end” did not mean legal termination. It is difficult to carry forward emergency authority while treating the emergency’s endpoint as politically useful but legally irrelevant.

That is why the transition from Midnight Hammer to Operation Epic Fury carries the most precedential weight. Midnight Hammer relaxed the target constraint, but still appeared to preserve a mission and time constraint. Epic Fury required the administration to soften that remaining boundary.

Epic Fury Turned a Prior Episode Into an Ongoing Conflict

The State Department’s April 21, 2026 legal memorandum on Operation Epic Fury supplied the key move. It advanced an “ongoing international armed conflict” theory for U.S. action against Iran, treating the February-to-April 2026 operation as legally connected to a continuing conflict rather than as a new use of force needing its own armed-attack trigger.[5]

That formulation changes the work a lawyer has to do. If the United States is responding to a new armed attack, the analysis must identify that attack and test necessity, proportionality, attribution, and timing around it. If the United States is already in an ongoing international armed conflict, the memo can place more weight on continuity: prior hostilities, prior defensive claims, and the law governing conduct within an existing conflict. The pressure point moves from initiation to characterization.

A former State Department legal adviser’s critique in Just Security challenged the State Department memorandum’s international-law reasoning, including the way it handled the claimed ongoing conflict and the relationship between earlier events and later force.[6] The disagreement is not merely about labels. Once “ongoing conflict” does enough work, the administration can reduce the legal significance of gaps between operations, presidential declarations of closure, and the absence of a new congressional vote.

The hard question is not whether international law recognizes any continuing armed conflicts. It does. The harder question is whether this record supports the continuity claimed. A prior limited collective-defense strike, followed by a presidential statement that the conflict was at an “Official END,” is not an easy foundation for a later theory that the conflict never meaningfully ended. The administration may have had operational reasons to prefer continuity; the legal consequence is that continuity can make a new authorization question disappear.

This is the point at which legal authorization creep becomes visible. The earlier self-defense rationale does not have to be formally rewritten. It only has to be carried forward, supplemented, and recharacterized until the original limiting facts no longer control the later operation.

The International-Law Doctrines Did Not Remove the Domestic Authorization Gap

The administration leaned on international-law concepts that can support defensive force in some circumstances, but none of them supplied an affirmative congressional authorization. “Accumulation of events” can help explain why a state views repeated attacks as a larger armed attack. “Substantial involvement” can help argue that support to an armed group is legally attributable to a state. An ongoing-conflict theory can alter how later force is characterized. Each doctrine addresses a different legal problem, and each remains contested at the margins relevant here.[3][4][5][6]

Even if one accepted parts of the international-law account, the Article II problem would remain. The March 28 letter claimed presidential power. It did not claim that Congress had authorized war with the Houthis, much less Iran.[1] Midnight Hammer and Epic Fury then pushed the claim across actor, purpose, and time. Domestic law does not become less important because the executive branch has found a more capacious international-law vocabulary.

For a fuller treatment of the UN Charter self-defense objection to the Iran strikes, see US-Israeli strikes on Iran failed the UN Charter self-defense test. The question here is narrower: how a sequence of legal predicates became usable inside the U.S. constitutional war-powers file.

Congress Objected, but the Mechanism Did Not Bite

Congress did have formal moments to respond. On June 23, 2026, the Senate voted 50-48 to join the House in passing a War Powers Resolution concurrent resolution directing removal of U.S. forces from hostilities involving Iran. Reuters and NPR both reported that this was the first time both chambers had passed such a concurrent resolution directing troop removal under the War Powers framework.[7][8]

That should have been institutionally significant. It was bicameral. It was specific to the Iran hostilities. It put Congress on record against the continuation of the operation. But the administration treated it as nonbinding, relying on the post-Chadha defect in legislative-veto mechanisms. Since INS v. Chadha in 1983, a concurrent resolution that is not presented to the President is unlikely to have binding legal effect.[7][8]

This is where the War Powers Resolution’s architecture becomes least satisfying for anyone who still wants it to operate as a restraint. A concurrent resolution can register institutional opposition, create political costs, and supply evidence for later litigation or oversight. But if the executive branch can disregard it as legally unenforceable, it does not stop the operation. It becomes part of the record, not a brake.

The funding record created a second problem. The administration sought an $80 billion Pentagon supplemental request, and Congress did not cut it. Lawfare’s analysis of Operation Epic Fury treated that uncut request as relevant to implied-consent analysis under Dellums v. Bush, where congressional funding and related conduct may bear on whether Congress has effectively acquiesced in a military operation.[9]

That does not mean every defense appropriation authorizes every conflict. It means the record is messy in a way that favors executive continuity. Congress can pass a nonbinding removal resolution with one hand and leave operational funding intact with the other. In later litigation, the executive branch does not need to prove that Congress enthusiastically authorized the operation; it can argue that Congress knew, objected through a mechanism it could not enforce, and still declined to use the funding tool that would have had practical force.

That is a constitutional mechanism problem, not a partisan scorecard. The War Powers Resolution offers a vocabulary of reporting and withdrawal. Chadha limits the legal effect of the concurrent-resolution device. Appropriations practice then risks turning inaction into legible consent. The result is a system in which Congress can be formally present and practically ineffective at the same time.

The broader Iran war-powers conflict is examined separately in How the Iran War Is Testing Constitutional War Powers. The narrower point here is that Congress’s two most visible tools—withdrawal direction and funding control—did not interrupt the administration’s Article II chain.

What the Sequence Leaves Behind

The precedent is not any one strike. A narrow defensive strike can be defended or criticized on its own facts. A limited collective-defense operation can rise or fall on a different set of facts. An ongoing-conflict memorandum can be tested against the record it claims to describe. The more durable problem is what happens when all three are placed in sequence.

In March 2025, the administration claimed Article II self-defense against Houthi attacks without statutory authorization or a Security Council mandate.[1] In June 2025, the theory reached Iran through a limited collective-defense frame. By April 2026, the State Department characterized the matter as an ongoing international armed conflict, even though the public record included Trump’s declaration that the June conflict had reached an “Official END.”[5][6] Congress then passed the first bicameral War Powers concurrent resolution directing troop removal, but the administration treated it as nonbinding after Chadha, while the $80 billion supplemental remained uncut.[7][8][9]

That chain is the legal authorization analysis that matters. Self-defense supplied urgency. Collective defense widened the target. Ongoing conflict softened the clock. Congressional inaction on funding gave the executive branch an implied-consent argument after Congress’s formal objection failed to bind. None of those moves alone had to announce a general war-making power. Together, they built reusable infrastructure.

Future executive lawyers will not need to cite this episode for the proposition that the President can do anything. They will cite the smaller propositions: delayed notice did not stop the Houthi operation; a limited collective-defense strike against Iran could follow; an ended conflict could still be described later as legally ongoing; a concurrent resolution did not bind; uncut funds helped show congressional acquiescence. Those are the carry-forward phrases that harden.

The institutional consequence is therefore narrower and more serious than a complaint about presidential aggressiveness. Congress had formal moments to object, including bicameral War Powers action and the funding process. Those moments did not practically restrain the Article II claim. The legal predicate became less constrained as the campaign continued, and the record now gives future officials a path for moving from urgent self-defense to continuing armed conflict without a new armed-attack predicate or affirmative congressional assent.

References

1. Text of a Letter from the President to the Speaker of the House of Representatives and the President Pro Tempore of the Senate, White House
2. White House Releases Letter Informing Congress of Houthi Strikes, Lawfare
3. Military and Paramilitary Activities in and Against Nicaragua, US Naval War College
4. The US and UK Military Strikes in Yemen and the Jus ad Bellum, International and Comparative Law Quarterly
5. Operation Epic Fury and International Law, U.S. Department of State, April 21, 2026
6. State Department’s Epic Fury International Law Analysis, Just Security
7. US Senate joins House in voting to halt Iran war, rebuking Trump, Reuters, June 23, 2026
8. Senate Iran war powers resolution, NPR, June 23, 2026
9. Operation Epic Fury Puts Congress and the Constitution to the Test, Lawfare