The United States Senate advanced legislation on Tuesday that seeks to force US President Donald Trump to withdraw from the Iran war, as a growing number of Republicans defied the president's direction on a conflict that has spanned well over two months.

Since Trump ordered the attack on Iran at the end of February, Democrats have forced repeated votes on war powers resolutions that would require him either to gain congressional approval or withdraw US troops. Republicans had been able to muster the votes to reject those proposals, but Louisiana Senator Bill Cassidy – fresh off a primary election loss in which Trump endorsed his opponent – switched sides.

The 50-47 vote tally showed that a small but growing number of Republicans are willing to challenge Trump on the Iran war, even though the effort may not advance much further. Three Republicans were absent on Tuesday and their votes would be enough to defeat the measure, if they maintain their stance on the war.

Still, the vote showed how Republicans are increasingly uneasy with a conflict that shows no signs of ending, is stuck in a fragile ceasefire and is causing rising gas prices in the US.

“Republicans are starting to crack, and momentum is building to check him,” Senate Democratic leader Chuck Schumer said in a statement after the vote. "We are not letting up.”

Republican Senators Rand Paul of Kentucky, Susan Collins of Maine and Lisa Murkowski of Alaska had all previously voted for similar war powers resolutions and did so again on Tuesday. Cassidy supported the legislation for the first time, while Senator John Fetterman of Pennsylvania was again the only Democrat to vote against it.

After his primary election loss last week, Cassidy returned to Washington defiant. He said he was proud of his work to uphold the Constitution and would carefully consider how he would vote on several priorities of the Trump administration going forward.

Trump's grip on the Senate Republican Conference is potentially slipping after Cassidy's primary loss, as well as the president's decision on Tuesday to endorse Republican Senator John Cornyn's primary opponent.

“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 on social media.

“Until the administration provides clarity, no congressional authorisation or extension can be justified.”

Across the Capitol, the House is expected to vote on a similar war powers resolution on Wednesday, and Democrats are bullish about their chances of passing it. Another war powers resolution barely failed in the House last week, the vote ending in a tie.

Even if Congress eventually passes legislation to compel Trump to withdraw from the conflict, it's not clear that he would comply. To circumvent requirements of the War Powers Resolution of 1973, the White House has claimed that it has technically ceased “hostilities” with Iran because there is a ceasefire.

Trump this week said he ordered preparations for an attack on Iran on Tuesday, only to call it off to give allies in the Gulf more time to work out an agreement with Iran.

“Peace negotiations are stuck and so day after day after day grocery prices climb, gas prices climb," Democratic Senator Chris Murphy of Connecticut said in a floor speech. (AP)



Edited by Cecil Wong