The war powers measure was rejected in a 53-47 vote largely along party lines. It would have halted US military action in Iran without congressional approval.

Democrats argue that Trump has sidelined Congress and offered shifting reasons for the war. Most Republicans blocked the resolution, but some said they could change course if the war expands in the coming weeks.

The US and Israel began striking Iran on Saturday. The Islamic Republic has responded by launching attacks on Israel and US-allied states in the Gulf.

With no clear off-ramp in sight, Defence Secretary Pete Hegseth said the war could last eight weeks – almost double the duration mentioned by Trump at the weekend.

Two senators crossed the aisle in Wednesday’s vote. Democratic Senator John Fetterman of Pennsylvania opposed the measure, while Republican Senator Rand Paul of Kentucky voted for it.

Otherwise, everyone else voted along party lines.

Senator Susan Collins, a moderate Republican from Maine, voted against the measure, saying afterwards that passing the legislation would have sent the wrong message to Iran and US troops.

“At this juncture, providing unequivocal support to our service members is critically important, as is ongoing consultation by the administration with Congress,” she said.

Senate Democratic leader Chuck Schumer said before voting in favour of the measure: “Do you stand with the American people who are exhausted with forever wars in the Middle East or stand with Donald Trump and Pete Hegseth as they bumble us headfirst into another war?”

The legislation will go to a vote in the House of Representatives on Thursday, where it faces an uphill battle.

While the president has broad authority to launch military action without a formal declaration of war, Congress must be notified within 48 hours of hostilities beginning.

Secretary of State Marco Rubio has maintained the Trump administration complied with that requirement.

Top congressional leaders were notified before the initial strikes began, and Trump informed Congress in a letter on Monday, even as he maintained that was not necessary.

Trump has previously ordered military operations without congressional approval, such as the US strikes against Iranian nuclear facilities last year, and the seizing of Venezuela’s President Nicolás Maduro in January.

“To begin with, no presidential administration has ever accepted the War Powers Act as constitutional – not Republican presidents, not Democratic presidents,” Rubio, a former senator, said.

Congress passed the War Powers Resolution in 1973 to constrain the ability of then-President Richard Nixon to wage war in Vietnam.

It requires lawmakers to be notified by the president within 48 hours of military action and for Congress to pass an Authorization for Use of Military Force (AUMF) within 60 days of hostilities breaking out.

Since 2001, US administrations have relied on the AUMF passed after the 11 September 2001 attacks as justification for the use of military force in the Middle East.

Multiple attempts to repeal that authorisation have been unsuccessful.

While Democrats were in favour of passing the bill, Republicans were divided and previously voted it down.

The package includes $60bn for Kyiv, $14bn for Israel’s war against Hamas and $10bn for humanitarian aid in conflict zones, including in Gaza.

Lawmakers voted 70 to 29 to approve the package.

The bill will now go to the Republican-controlled House of Representatives, where its fate remains uncertain.

The package, which also includes more than $4bn in funds for Indo-Pacific allies, passed the Senate despite criticism from Republican House Speaker Mike Johnson and former President Donald Trump.

In the end, 22 Republicans voted for the legislation including Senate Minority Leader Mitch McConnell.

“History settles every account,” Mr McConnell said in a statement following the vote. “And today, on the value of American leadership and strength, history will record that the Senate did not blink.”

Ukraine’s president also said he was “grateful” to senators for passing it.

“For us in Ukraine, continued US assistance helps to save human lives from Russian terror. It means that life will continue in our cities and will triumph over war,” Ukraine’s President Volodymyr Zelensky wrote in a post on X, formerly known as Twitter.

The vote came after an all-night Senate session during which several Republicans made speeches criticising the measure.

The aid package is a stripped down version of a $118bn package that Senate Republicans voted down last week.

Republicans had initially demanded that any foreign aid be tied to more security measures at the southern border.

But after Mr Trump came out against the measure, Republicans were divided on the package.

Some lawmakers suggested that border security measures could be added back into the current version of the legislation.

Mr Johnson suggested in a statement on Monday night that the new bill would not pass the House without such provisions.

“House Republicans were crystal clear from the very beginning of discussions that any so-called national security supplemental legislation must recognise that national security begins at our own border,” he said.

Mr Johnson claimed lawmakers “should have gone back to the drawing board” with the legislation to focus on border security provisions.

Democratic Senate Majority Leader Chuck Schumer, meanwhile, hailed the passage of the bill on Tuesday. He said the Senate was “telling Putin he will regret the day he questioned America’s resolve”.

The US is one of the largest providers of aid to Ukraine. The White House asked Congress months ago to pass a bill that included foreign aid.

This could be Congress’s last shot at passing Ukraine aid for the foreseeable future, and Ukraine has warned that it may not be able to successfully defend itself against Russia without Washington’s backing.