The Senate on Tuesday advanced a resolution to halt military action in Iran after a surprise defection from Republican Sen. Bill Cassidy of Louisiana, dealing a blow to President Donald Trump's war effort.

The vote, though preliminary, shows that the Senate now could have the votes to force Trump to pull back the military from Iran or seek congressional approval for additional action.

Despite the War Powers Resolution advancing 50-47, it still has little chance of becoming law. It would need to pass a final vote in the Senate, clear the House and Trump would be almost certain to veto it. But the vote does show increasing headwinds to the war with Iran, especially as gas prices continue to soar ahead of the summer driving season and the 2026 midterms.

Cassidy, who failed to advance to a runoff against Trump-endorsed challenger Rep. Julia Letlow, R-La., in a primary election last week, is now in the final months of his term in the Senate. His vote indicates that he is now more willing to challenge Trump.

"While I support the administration's efforts to dismantle Iran's nuclear program, the White House and Pentagon have left Congress in the dark on Operation Epic Fury," Cassidy said in a statement to his X account after the vote. "In Louisiana, I've heard from people, including President Trump's supporters, who are concerned about this war. Until the administration provides clarity, no congressional authorization or extension can be justified."

The war with Iran has now blown past the 60-day requirement under the War Powers Act for the president to seek the authorization of Congress for the use of military force. Though the Trump administration has challenged the law as unconstitutional, and claimed that a tenuous ceasefire in early April has stopped the clock by ceasing hostilities.

Republicans, who broadly opposed the measure, may have also been hindered by absences that allowed the measure to proceed. Several senators, including Sens. Thom Tillis, R-N.C., John Coryn, R-Texas and Tommy Tuberville, R-Ala., were absent from the vote.

Sen. John Fetterman, D-Pa., was the sole Democrat to vote against the measure, while 46 Republicans voted for it.

Democrats in the House and Senate have pushed more than a dozen war powers resolutions since the war in Iran started. So far, all have been defeated. Some Republicans in Congress, however, have begun to support requiring the administration to seek approval from Congress after the conflict surpassed the 60-day point. Congress has the sole authority to declare war, according to the Constitution.

The war, which has nearly reached the three-month mark, has wreaked havoc on the global economy and spiked oil prices in the U.S. Iran has largely held the Strait of Hormuz shut for the duration of the war, a key channel which carries about a fifth of the world's oil.

Gas prices in the U.S. are now more than $4.53 per gallon on average, according to AAA.