May 20 (Reuters) – The U.S. Senate advanced a war-powers resolution on Tuesday that would end ​the Iran war unless President Donald Trump obtains Congress’ authorization, a rare rebuke of the Republican leader 80 days after ‌U.S. and Israeli forces began striking Iran.

The vote on a procedural measure to advance the resolution was 50 to 47, as four of Trump’s fellow Republicans voted with every Democrat but one in favor. Three Republicans missed the vote.

The result was a victory for lawmakers who have been arguing that Congress, not the president, should have ​the power to send troops to war, as spelled out in the Constitution. However, it was only a procedural vote, and ​the resolution faces steep hurdles before going into effect.

Even if it eventually passes the 100-member Senate, the resolution ⁠must also pass the Republican-led House of Representatives and garner two-thirds majorities in both the House and Senate to survive an expected Trump ​veto.

Democratic Senator Tim Kaine of Virginia, who sponsored the resolution, said a ceasefire offered Trump an ideal opportunity to make his case to Congress ​as the president has said Tehran has made a new proposal to end the U.S.-Israeli war that began on February 28.

“That’s the perfect time to have a discussion before we start up war again. The president is receiving peace and diplomatic proposals that he is throwing into the trash can without sharing them with us,” Kaine ​said during debate before the vote.

Trump’s Republicans blocked seven previous attempts to advance similar resolutions in the Senate this year. They have also stopped three ​war-powers resolutions by narrow votes in the House this year.

Senator John Fetterman of Pennsylvania was the only Democrat to vote against the measure. Republicans Rand ‌Paul of ⁠Kentucky, Susan Collins of Maine and Lisa Murkowski of Alaska voted in favor, as did Senator Bill Cassidy of Louisiana, days after he lost his primary to an opponent backed by Trump.

The war-powers vote was the second in the Senate since the conflict hit a deadline on May 1, 60 days after Trump formally informed Congress that the conflict had started, for Trump to come to Congress about the war.

Under a 1973 U.S. ​war-powers law passed in response to ​the Vietnam War, a U.S. president ⁠can wage military action for only 60 days before ending it, asking Congress for authorization or seeking a 30-day extension due to “unavoidable military necessity regarding the safety of United States Armed Forces” while withdrawing forces.

Trump declared ​on May 1 that a ceasefire had “terminated” hostilities against Iran.

Despite that assertion, the U.S. has been blockading ​Iranian ports and ⁠striking Iranian ships, and Iran has been effectively blocking the Strait of Hormuz and attacking U.S. ships.

Democrats, and a few Republicans, have called on Trump to come to Congress for authorization to use military force, noting that the U.S. Constitution says that Congress, not the president, can declare war. They have ⁠expressed concerns ​that Trump may have entered the country into a long conflict without setting out ​a clear strategy.

Republicans, and the White House, say Trump’s actions are legal and within his rights as commander in chief to protect the U.S. by ordering limited military operations.

Some congressional ​Republicans have accused Democrats of filing the war-powers resolutions only because of their partisan opposition to Trump.