Washington, DC – The United States Senate has failed to pass a resolution seeking to rein in US President Donald Trump’s war with Iran.

The latest war powers resolution failed 47 to 52 in a procedural vote, marking another major setback for proponents of curtailing Trump’s military pursuits abroad and underscoring Republicans’ embrace of the president’s campaign.

A separate resolution is set to be voted on in the US House of Representatives on Thursday, but it too faces stiff odds.

Lawmakers in the Senate had spent the day arguing for and against asserting Congress’s powers to authorise or end Trump’s military actions against Iran.

Supporters of the resolution say Trump exceeded his constitutional authority by launching a war alongside Israel. Under Article II of the US Constitution, presidents can only launch such attacks in self-defence in response to an immediate threat. Otherwise, Congress has the sole power to declare war.

Speaking on the Senate floor, Senator Tim Kaine argued that, “even in a classified setting”, the Trump administration “could produce no evidence, none that the US was under an imminent threat of attack from Iran”.

“You can’t stand up and say: This is a pinprick that doesn’t lead to the level that would be characterised as war,” Kaine said. “You can’t stand up and say: This is one and done, and no troops are engaged in hostilities against Iran.”

Republicans rally behind Trump

Since launching its military offensive on February 28, the Trump administration has offered a carousel of rationales for why a war was needed now.

Trump has suggested that Iran was seeking to rebuild its nuclear programme, which he has said was “obliterated” in strikes last year. He also said that Iran was seeking to develop a long-range missile to attack the US.

Secretary of State Marco Rubio, meanwhile, told reporters that Israel was planning to attack Iran, which would likely have led to retribution against US assets in the region. Trump later contradicted the claim, saying Iran was the one planning an imminent attack on Israel.

To undergird those claims, the Trump administration has also sought to frame the whole of Iran’s military and nuclear-energy programmes since the Islamic revolution in 1979 as an immediate threat to the US.

Several Republicans spoke out against the resolution, arguing that the last 47 years of sabre-rattling from Iran justified the president’s military action.

The Constitution, according to Senator James Risch, “clearly gives the president not only the right, but indeed the duty, as does his oath to protect the United States”.

Risch also pointed to Iran’s efforts to rebuild its nuclear energy assets after a US attack in June of last year, conducted as part of a 12-day war led by Israel.

“The commander-in-chief ordered this attack because of the increase in the manufacturing of long, medium-range missiles — and after [Iran tried] to restart the nuclear programme that was decimated in the 12-day war,” Risch said.

The US and Iran had been in the middle of negotiations to scale down Iran’s nuclear programme in the lead-up to this month’s war, but Risch dismissed those efforts as performative.

“All this time, they had us sitting at the table, dragging out and yakking away at negotiations that were going absolutely nowhere,” he told the Senate, calling on his fellow lawmakers to vote down Wednesday’s resolution.

The vote, which broke down largely along party lines save for one Republican and one Democrat breaking ranks, was the latest in a series of war powers resolutions to fail in Congress. Since the June 21 attack, Congress has introduced several measures to stop Trump from carrying out military campaigns in Iran and Venezuela, to no avail.

Under the 1973 War Powers Act, US presidents must seek congressional approval after committing US troops to military actions for more than 60 days.

Earlier on Wednesday, Pentagon chief Pete Hegseth argued that the US operation had just begun, with more US assets being sent to the region.

The duration and scope of the conflict remain unclear, though Trump himself has projected it could last “four to five weeks”. Still, Risch expressed optimism that the conflict would be resolved quickly.

“This is going to end, and it’s going to end rapidly. This is not a forever war, indeed, not even close to it,” Risch said. “This is going to end very quickly.”

Why war powers votes still matter

Even if Wednesday’s effort had passed, the Senate’s war powers resolution would have faced an uphill battle before it could become law.

Both chambers would have needed to pass the resolution for it to go to the president’s desk for a final signature — but even then, Trump could have vetoed the measure.

Only a two-thirds majority in both chambers can override a presidential veto.

Still, advocates have long maintained that such resolutions force lawmakers to confront important questions about the limits of presidential power, even if they are long shots.

They also give constituents a reason to petition their elected officials and voice their concerns about the war.

“While the outcome did not pass, this moment underscores a core truth: Congress must continually reassert its constitutional role to check executive power and prevent endless wars,” said Hassan El-Tayyab, the legislative director for Middle East policy at the Friends Committee on National Legislation, a Washington-based nonprofit.

“Our founders warned that unchecked authority leads to unchecked conflict. Senators and Representatives must keep forcing votes to curb US military engagement in unauthorised wars.”

Cavan Kharrazian, a senior policy adviser for the advocacy group Demand Progress, also pointed out that congressional votes can help inform the electorate about their representatives’ stances on key issues.

That, in turn, can have political consequences at the ballot box, particularly in an election year.

“The American people will remember who voted to continue an illegal, unnecessary war,” Kharrazian said.

“Every senator who voted against the war powers resolution also voted against the wishes of the American people and against the safety of the servicemembers they are sworn to protect. The stakes are clear, and there is no more time for political games.”