The United States Senate has passed a bill to pause President Donald Trump’s military campaign against Iran and seek congressional approval before any further action is taken.
On Tuesday, the chamber voted 50 to 48 to pass the resolution, which had been approved in the House of Representatives earlier in the month.
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Republicans hold a majority in the Senate, but four conservatives crossed party lines to approve the resolution, along with nearly all the chamber’s Democrats, save one.
Tuesday’s vote marked the first time a war powers resolution had successfully passed both chambers of Congress. But the effort is likely to be symbolic, as Trump is expected to veto the measure.
Tuesday’s breakaway Republicans included Bill Cassidy of Louisiana, Lisa Murkowski of Alaska, Susan Collins of Maine and Rand Paul of Kentucky. A further two Republicans did not vote: Mitch McConnell of Kentucky and Dave McCormick of Pennsylvania.
The lone Democrat to side with Republicans on the matter was Pennsylvania’s John Fetterman.
Speaking on the chamber floor, top Democrat Chuck Schumer noted that Tuesday’s vote marked the 10th time the Senate had taken up a war powers resolution to rein in Trump’s military campaign against Iran.
“For years, Trump promised to put maximum pressure on Iran, but he ended up delivering maximum confusion, maximum chaos, maximum cost to the American people with his disastrous war,” Schumer said.
“ Time after time, the vast majority of Senate Republicans sided with Trump and his war, instead of the American people. The American people have paid the price for Trump’s historic blunder in Iran. It’ll go down in the history books as one of the worst foreign policy forays America has ever made.”
Concerns about war negotiations
On February 28, Trump joined Israel in launching attacks against Iran, triggering a region-wide war that has continued through this month.
It was also the second time since returning to office for a second term that Trump involved US military forces in a war against Iran. In June 2025, Trump had also sent bombers to attack three key sites associated with Iran’s nuclear enrichment programme.
Trump has said the latest war was necessary to prevent Iran from developing a nuclear weapon, an ambition it has long denied.
But critics have characterised the February strikes as an unprovoked act of aggression that has threatened to further destabilise the Middle East.
Negotiations are currently underway in Switzerland, as the Trump administration and Iran continue to discuss the terms of a ceasefire set out in a June 17 memorandum of understanding (MOU).
But whether that memorandum will hold remains unclear. Israel, the US’s partner in the war against Iran, has continued to carry out strikes in Lebanon, violating the terms of the agreement, which called for a halt to fighting on all fronts.
Critics of Tuesday’s resolution pointed to the ongoing negotiations as a reason to scuttle the bill’s passage.
The war powers resolution “directs the President to remove United States Armed Forces from hostilities against the Islamic Republic of Iran”.
Only if “explicitly authorised by a declaration of war or a specific congressional authorisation” would Trump be allowed to use further military force against Iran.
The resolution, however, does allow for limited military presence to remain in the Middle East, in order to prevent any “imminent attack” against the US or its allies.
Still, some Republican senators warned the war powers resolution would weaken Trump’s standing in the Switzerland negotiations.
“If this passes, the Iranians are going to simply stand up and walk away from negotiations,” James Risch of Idaho told the Senate chamber.
“They’re going to say: This thing’s over. The Congress has told the President of the United States, ‘Leave us alone. We can do whatever we want to do.’ And they will walk away.”
Risch also argued that the resolution was essentially useless, given the all but certain prospect of Trump’s veto. “It’s going to have no effect. The president isn’t going to pay any attention to it,” he said.
Growing pressure on Trump
Still, the bill’s passage shows a growing congressional consensus against the president’s use of military force.
The war against Iran has been widely unpopular in the US. A poll released on Tuesday by the media outlet Reuters and the research firm Ipsos found that only 24 percent of US citizens felt the war had been worth the cost.
Prices for essential supplies like oil, natural gas and fertiliser have spiked since the war began, as a result of the Iranian blockade in the Strait of Hormuz and the US response.
Republicans are also facing pressure from voters ahead of November’s heated midterm elections, which will decide whether the right-wing party will maintain its control over both the House and Senate.
In the US, the Constitution gives Congress the sole power to declare war, but that division of power has eroded over the last 75 years, as successive presidents have committed US forces to overseas conflicts.
Trump has pointed to that precedent to argue that he does not need congressional authorisation at all.
In an appearance on The Axios Show last week, Trump denied learning any “lesson” about the limits of his executive powers during the Iran war. “There are no limits,” he said.
The last time Congress voted to declare war was during World War II, though it has passed authorisations for the use of military force (AUMFs) in the decades since, which allow for limited military engagement.
Some critics point out that Republicans may be more willing to confront Trump over the issue of congressional authorisation now, as they defend their seats in the midterms.
Others are in their final months in office, after being defeated by Trump-backed challengers. That is the case for Louisiana’s Senator Cassidy, who has shown more willingness to stand up to Trump’s agenda since his May 16 primary defeat.
A constitutional dilemma
The Senate passed its first war powers resolution against the Iran conflict on May 20, but that effort came right before a congressional recess, and it did not pass both chambers.
Tuesday’s successful vote picked up a similar measure already passed in the House of Representatives on June 3 by a vote of 215 to 208.
Democratic Senator Tim Kaine has long advocated for such a measure to pass both chambers. He reflected on the significance of Congress seeking to reclaim its constitutional powers over the ability to declare war.
“ The most solemn power for Congress is Congress has the power to declare war, not the president,” Kaine said.
He explained that the country’s founders understood that “ the stakes and consequences of war were so vast that a decision about war should never be in the hands of a single person, but instead should be vested in the legislative branch”.
Both he and Schumer pledged to keep pursuing war powers legislation until they were successful in reining in the president’s military campaigns.
“ Trump won’t brief Congress. Trump won’t defend his deal. Trump won’t end his war,” Schumer said.
“But Democrats will keep forcing this vote, and we’re going to keep doing it because only Congress has the power to take this nation to war, and this one must end.”
