The Senate passed a bipartisan war powers resolution Friday afternoon by a vote of 56 to 43, requiring President Donald Trump to seek congressional authorization for continued combat operations against Iran and delivering the sharpest institutional rebuke of the administration’s six-week war since hostilities began.

The resolution, sponsored by Sens. Tim Kaine, D-Va., Mike Lee, R-Utah, and Chris Murphy, D-Conn., directs the president to terminate the use of U.S. armed forces in hostilities against Iran within 30 days unless Congress affirmatively authorizes their continuation through a declaration of war or a specific use-of-force authorization. The measure carves out narrow exceptions for the defense of forces already deployed and for the protection of U.S. citizens and diplomatic facilities under imminent threat.

Eight Republicans joined every Senate Democrat and both independents in support of the measure, well clear of the simple majority required under the expedited procedures available to such resolutions. The eight Republicans included Lee, Sens. Susan Collins of Maine, Lisa Murkowski of Alaska, Rand Paul of Kentucky, Todd Young of Indiana, Bill Hagerty of Tennessee, Jerry Moran of Kansas, and a final crossover — Sen. Pete Ricketts of Nebraska — whose vote was not confirmed until the roll was called.

Kaine, speaking on the floor moments after the vote, framed the result as a constitutional inflection point. “For six weeks, this body has watched a war it never voted on grow into a war that has killed more than 360 of our service members,” Kaine said. “Today the Senate did the one thing the Constitution requires it to do. The House will now have its turn, and the country will be watching.”

The resolution now heads to the House, where Speaker Mike Johnson, R-La., has declined to commit to a floor vote. Under the War Powers Act, the measure is eligible for expedited consideration and cannot be indefinitely bottled up in committee, though leadership retains scheduling latitude. A senior House Democratic aide, granted anonymity to describe internal strategy, said House sponsors led by Rep. Ro Khanna, D-Calif., expected to force the question to the floor within two weeks regardless of the speaker’s preference.

White House Press Secretary Karoline Leavitt, briefing reporters within an hour of the vote, said the president would veto the resolution if it reached his desk in its current form. “This resolution would tie the president’s hands at the exact moment when the diplomatic track in Islamabad is most fragile and when the safety of our deployed forces depends most on operational flexibility,” Leavitt said. “The president believes deeply that Congress has a constitutional role here. He does not believe this resolution is the way to express it.”

Leavitt declined to specify whether the administration would support an alternative authorization, saying only that the White House was “in active conversation” with Senate and House leaders about “a more workable vehicle.” Two administration officials, speaking on condition of anonymity, said the National Security Council had circulated internal draft language Wednesday for a narrower authorization tied to a 90-day window and explicit objectives, though it had not yet been shared with congressional leadership.

The resolution’s passage capped a week in which several Senate Republicans publicly broke with the administration’s prosecution of the war for the first time. Murkowski said on the floor Friday morning that “circumstances have changed and so has my vote.” Hagerty, a former U.S. ambassador to Japan and a reliable administration ally on most foreign-policy questions, said he supported the resolution “because Congress has not done its job, and I will not pretend otherwise.”

Senate Majority Leader Chuck Schumer, D-N.Y., who had spent the previous 48 hours coordinating floor strategy with both the Kaine-Lee-Murphy team and a small group of skeptical Republicans, called the vote “the Senate at its best — slow, late, but eventually doing what the framers expected of it.” Schumer said he would move next week to bring the $67.4 billion war supplemental to a floor vote with the Appropriations Committee’s conditions intact.

The parallel diplomatic track in Islamabad shadowed Friday’s debate. Mediators from Pakistan, Saudi Arabia and Egypt have spent the week pressing Iran and the United States on a framework envisioning a phased halt to hostilities, and Iranian Foreign Minister Abbas Araghchi signaled earlier in the week a willingness to discuss a conditional pause. Senate aides said the resolution’s timing had been calibrated, in part, to strengthen U.S. negotiators’ leverage.

Lee, a longtime advocate for stricter constitutional limits on executive war-making, rejected the administration’s argument that the resolution would weaken the diplomatic track. “The strongest possible signal we can send to Tehran is that the American people, through their Congress, want this war to end on terms that protect our forces and our interests,” Lee said. “That signal is louder, not softer, when Congress speaks.”

Reema Khoury, a senior fellow at the Stimson Center and a former Senate Foreign Relations Committee aide, called the vote “the first clean institutional moment of this war.” She added: “The Senate has now placed itself on the record as a co-equal branch, and the House will be unable to avoid that posture for long.”

The Pentagon updated its casualty figures shortly after the Senate vote. Spokeswoman Sabrina Singh told reporters that the cumulative U.S. service-member death toll since the start of hostilities had reached 364, with more than 1,290 wounded. Singh said two additional fatalities had been confirmed Friday morning from a rocket attack on a position in southern Iraq overnight.

Vice President JD Vance, who had spent the week shuttling between Senate offices in an effort to hold the Republican caucus, was not present for the final vote. A Vance aide said the vice president had returned to the White House by late Friday morning for a meeting on the Islamabad framework. Two senators who had spoken with Vance earlier in the week said he had not asked them to vote against the resolution, only to delay their public position until an administration alternative could be circulated.

Outside the Capitol after the vote, a coalition of veterans’ groups and military family organizations held a brief rally on the East Front. Murphy joined the gathering and told organizers that “Congress finally did its job today, and tomorrow we go to work on the House.”

Senate aides said floor consideration of the war supplemental would begin Tuesday. The White House said the president’s response to the war powers resolution would be announced “in the coming days.”