Lisa Murkowski

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.

With one G.O.P. senator absent on Wednesday, the measure would have passed had Mr. Fetterman not voted with Republicans.

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.

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