The Senate on Wednesday blocked Democrats’ seventh attempt to halt the war in Iran, as Republicans banded together almost unanimously to beat back the first such effort since President Trump blew past a 60-day deadline to seek congressional authorization to continue the fighting.
But another Republican who had opposed earlier attempts defected from the party line on Wednesday, in a sign of growing cracks in the G.O.P.’s patience with the conflict and the president’s handling of it.
Senator Lisa Murkowski of Alaska for the first time joined Senators Susan Collins of Maine and Rand Paul of Kentucky in voting with Democrats to advance the measure. The effort failed on a vote of 50 to 49, with Senator John Fetterman of Pennsylvania again joining Republicans in opposition, casting the deciding vote to block the resolution.
Ms. Murkowski was the latest Republican to flip in recent weeks; Ms. Collins, who had opposed similar resolutions since the war began in late February, switched her vote earlier this month and joined Democrats and Mr. Paul in support.
A similar measure narrowly failed in the House last month. Such resolutions have little hope of enactment given Mr. Trump’s vehement opposition and veto power. But Democrats have vowed to continue to force the votes, eager to force Republicans to weigh in repeatedly on what polls show is an unpopular war whose cost poses political perils ahead of the midterm elections.
The White House has said hostilities with Iran terminated on the day the war reached its 60-day mark, and Defense Secretary Pete Hegseth reiterated Tuesday that even if the president were to restart bombings, he would not seek permission from Congress.
But Democrats and a small contingent of Republicans rejected the claim that hostilities had ended, pointing to recent exchanges of fire in the Strait of Hormuz, and the continued deployment of some 50,000 troops to the region.
Ms. Murkowski said it did not appear that hostilities had ceased, as the administration has claimed, “nor that anything has really changed much other than the words that are being used.”
For weeks, she has been working with like-minded Republicans who are concerned about an unauthorized war on a draft authorization that would limit the operation and force the president to develop exit criteria. But she said that effort, which faces procedural challenges, is on pause until a lapse in the cease-fire.
“Until then, I will support measures to officially end hostilities and bring our men and women home,” she added in a statement. “I will oppose any effort to redefine ‘hostilities’ in ways that allow the president to wage war indefinitely without seeking congressional approval as outlined by the Constitution.”
Democrats on Wednesday called on more Republicans who have continually voted against war powers resolutions to, like Ms. Murkowski, reject the president’s attempt to bypass the war powers law by citing a cease-fire that has not halted all military activity.
“Both sides are engaged in a daily war, as defined by international law,” said Senator Jeff Merkley of Oregon, the Democrat who sponsored Wednesday’s war powers resolution. “Is it at a somewhat lower level than the bombing campaign? Yes, I will grant you that. But it is a war by every definition.”
Still, the vast majority of Republicans indicated agreement with the administration that the current cease-fire with Iran means the hostilities the president notified Congress of on March 2, beginning the 60-day countdown to the president needing to ask Congress to approve continued combat operations, had ended.
“The president made it very clear,” Senator John Barrasso of Wyoming, the No. 2 Senate Republican, said on Wednesday. “Clear that the major fighting has halted, clear that the American cease-fire has held for more than a month.” He accused Democrats of “obstructing the president.”
Like Ms. Collins and Ms. Murkowski, Senator John Curtis, Republican of Utah, had said attacks on Iran must begin to wind down unless Congress provided formal authorization. But he voted against forcing an end to the war on Wednesday.
“I wouldn’t say I’m totally resolved in my mind,” Mr. Curtis said before casting his vote. “But we are in a cease-fire, and I want to see how this thing plays out.”
Democrats noted that the White House had provided no public evidence that Iran was poised to launch a nuclear attack on the United States, as the president, his cabinet officials and his G.O.P. allies in Congress have claimed was the rationale for launching joint attacks with Israel on Tehran on Feb. 28.
Senator Tim Kaine of Virginia, a member of the Armed Services Committee, said there was no threat of “any action anytime soon by Iran” to develop nuclear weapons that justified a wide-scale military operation.
“I don’t use this phrase a lot,” said Mr. Kaine, the Democrat leading the effort to force weekly votes on ending the war. “The White House has lied to the American public, and every time they say this war is justified to stop Iran’s nuclear program, they are telling the American public a lie.”
