The Senate voted 54-46 on Tuesday evening to adopt a war powers resolution declaring that any renewed U.S. military action against Iran must receive prior congressional authorization, a wider-than-expected bipartisan margin that handed President Trump the first significant institutional rebuke of his second-term foreign policy and reshaped the Capitol’s calculus on the $89.4 billion emergency war supplemental still awaiting its first markup.

Six Republicans joined every Democrat and both independents in supporting the measure, which had been introduced in mid-March as a symbolic protest and rewritten three times in the days after the April 15 Islamabad ceasefire. The Republican defectors were Senators Rand Paul of Kentucky, Lisa Murkowski of Alaska, Susan Collins of Maine, Todd Young of Indiana, Jerry Moran of Kansas and Mike Lee of Utah — a coalition that crossed the chamber’s libertarian, institutionalist and Appalachian-isolationist factions and that aides on both sides said had not voted together on a foreign policy question since the Yemen resolution of the first Trump term.

Senate Majority Leader John Thune, who had urged Republican senators in a closed-door conference lunch on Monday to “hold the line until the ceasefire holds 30 days,” accepted the result on the floor with a single sentence. “The Senate has voted; the House will have its say,” Thune said before moving to the supplemental schedule. Aides said the leader had counted at most four Republican defections going into the day and had been “blindsided” by Moran and Lee.

The resolution, sponsored by Senators Tim Kaine of Virginia and Chris Murphy of Connecticut, would require the president to seek a specific authorization from Congress before ordering offensive military operations against Iranian territory, Iranian forces outside Iranian territory or Iranian-flagged vessels in the Persian Gulf or Gulf of Oman. It carves out self-defense responses to direct attacks on U.S. personnel and a 14-day post-attack window during which the executive may act without prior approval, language that several Republican aides described as the threshold that had moved Moran and Young into the yes column over the weekend.

President Trump, asked about the vote as he left a Rose Garden event on small-business tax policy, called the resolution “a piece of paper from people who didn’t end the war” and said he would veto the measure if it reached his desk. “I brought 38 Americans home from Doha; I brought the troops home from a war that started before they got their first cup of coffee,” Trump said. “The Senate can pass whatever it wants. The Constitution doesn’t change.”

A White House statement of administration policy released 40 minutes after the vote called the resolution “constitutionally infirm and operationally reckless” and said the measure would, if enacted, “tell the ayatollah he has 14 days to rebuild before the president can lift a finger.” The statement did not directly threaten a veto but referred to “every option available to the executive.”

The House math is the more important number. Speaker Mike Johnson, in a written statement issued shortly after the Senate vote, said the resolution would be referred to the House Foreign Affairs Committee and that “the regular order” would apply, language that Democratic aides read as a signal he intended to slow the resolution rather than bring it directly to the floor. Discharge petitions to force a floor vote would require 218 signatures; Democrats hold 213 seats, leaving Minority Leader Hakeem Jeffries five votes short before any defections.

Representative Don Bacon of Nebraska and Representative Brian Fitzpatrick of Pennsylvania, both members of the bipartisan Problem Solvers Caucus, told reporters in the Speaker’s Lobby Tuesday afternoon they would “look hard” at signing a discharge petition if one was filed. Representative Marc Molinaro of New York went further, telling NY1 in an interview taped before the Senate vote that he would sign “today” if the petition were available. None of the three has publicly committed to a yes vote on the underlying resolution.

“The arithmetic isn’t there yet, but the gravity is,” said John Lawrence, a former chief of staff to Speaker Nancy Pelosi who now teaches at the University of California, Washington Center. “When six Senate Republicans cross on a war vote, House members in suburban swing districts read the polling the same way the senators did. The Speaker’s problem is not next week; his problem is whether he can keep this off the floor through the Memorial Day recess.”

The resolution’s adoption complicates the parallel fight over the supplemental. Senate Appropriations Chair Susan Collins, who voted for the resolution, told reporters Tuesday she still expected the supplemental to clear her committee by Friday, but said she would now seek to add an explicit reporting requirement tying any future drawdown of replenished Patriot and SM-6 inventories to congressional notification within 48 hours. Ranking Democrat Jack Reed said the resolution’s passage gave appropriators “permission to attach the kind of guardrails the executive branch said last week were unnecessary.”

Democrats also reopened the question of an independent Iran war commission, which Representative Theresa Holloway of Michigan has been pushing since April 17. Holloway said in a hallway statement Tuesday evening that 196 members had now signed her discharge petition, up from 184 on Sunday, and that “today changed the conversation with at least a dozen more.” Aides said Holloway’s office expected to formally cross the discharge threshold in early May if current trajectories held.

Reaction from outside Washington tracked the political divide. The Foundation for Defense of Democracies called the vote “a self-inflicted wound at the precise moment Tehran is testing the ceasefire’s seams.” The Quincy Institute, which had lobbied moderate Republicans for two weeks, called the result “a long overdue restoration of the constitutional design.” A senior European diplomat, granted anonymity to discuss internal NATO conversations, said allied governments were “reading the vote as a domestic political event, not a policy shift,” but acknowledged it would factor into how Gulf mediators framed the next round of monitoring talks scheduled for Doha on May 11.

Brent crude, which has anchored near $94 for a week, was little changed in evening trading. The dollar weakened modestly against the euro. Treasury yields drifted lower as traders parsed the vote against Friday’s expected payrolls print and a Wednesday appearance by Defense Secretary Pete Hegseth before the Senate Armed Services Committee.

Senior administration officials said the president would not address the vote at his Wednesday schedule of events in Pennsylvania and Ohio, with one official saying the White House intended to “stay on the economic message” through the end of the week. Congressional aides on both sides of the aisle said they expected the House Foreign Affairs Committee to hold its first hearing on the resolution no later than the second week of May.