Washington, DC – The latest effort to curtail United States President Donald Trump’s power to wage war with Iran has failed in the House of Representatives by a slim margin.

Only a single vote on Thursday separated the yeas and nays, with 213 in favour and 214 against the latest war powers resolution.

The House vote did show increased consolidation among Democrats, signalling the increasingly entrenched view that the president is acting beyond his constitutional authority.

Three members of the party who had opposed a similar resolution in March — Juan Vargas, Greg Landsman and Henry Cuellar — this time supported the bill.

Only one Republican, the resolution’s co-sponsor Thomas Massie, voted to pass the resolution, while one Democrat, Jared Golden, voted against it.

A second Republican, Warren Davidson, who had supported reining in Trump’s power during last month’s vote, voted “present” as a way of not taking a position.

Republican Nancy Mace, who has increasingly questioned the war and its high price tag, also did not vote on Thursday.

The House defeat came a day after a similar resolution failed in the US Senate, by a vote of 52 to 47, mostly along party lines.

The twin votes have underscored Republicans’ continued wariness about constraining Trump’s war against Iran and his overall military involvement abroad.

Following Thursday’s failed vote, Democrats accused Republicans of giving unchecked power to Trump, who joined Israel in initiating strikes against Iran on February 28. The war has continued over the six weeks since, with ceasefire negotiations under way.

“Servicemembers have been killed, gas prices are soaring, and the US in a worse position than before,” Representative Bill Foster, a Democrat, said in a post on the social media platform X.

“Congress cannot abdicate its power as a co-equal branch of government and let this rogue President continue to unilaterally wage war.”

Under the US Constitution, only Congress can declare war, although presidents may conduct military actions in instances of immediate self-defence.

The Trump administration has maintained that Iran’s actions since the 1979 Iranian Revolution constitute such a threat. Critics, however, have argued that the US and Israeli attack on Iran was unprovoked, thereby violating international law.

Speaking before the vote, Republican Brian Mast decried the latest resolution as “crazy”, pointing to a two-week pause in fighting reached last week, which currently extends through April 22.

Mast also called it “hypocrisy” for Democrats to oppose Trump’s war in Iran, pointing to overseas strikes under Democratic presidents in countries like Yemen.

“When Joe Biden was responding to merchant marine vessels being attacked, it was OK. No war power needed,” Mast said.

Ceasefire negotiations over the Iran war are ongoing. The US and Iran have since signalled they are open to another round of talks in Pakistan, after initial negotiations over the weekend failed to yield a breakthrough.

There has been movement on at least one major obstacle: Iran’s insistence that the current ceasefire must also apply to Israel’s ongoing invasion of Lebanon.

On Thursday, Trump announced a 10-day pause in the fighting in Lebanon. The deal had been struck between the governments of Lebanon and Israel, but it was not immediately clear if Hezbollah, an Iran-backed group, had signed on to the plan.

Others issues, including control of the Strait of Hormuz and the future of Iran’s nuclear programme, remain unresolved.

There were also indications that the US was preparing to re-start military operations, should the ceasefire with Iran fail to hold. Pentagon chief Pete Hegseth said on Thursday the US was ready to resume attacks on Iran’s energy facilities, but that the Trump administration preferred diplomacy.

“Our forces are maximally postured to restart combat operations, should this new Iranian regime choose poorly and not agree to a deal,” he told reporters.

In a statement responding to the House vote, the antiwar group Demand Progress criticised both Republicans and Democrats for failing to pass the war powers resolution.

“Congress has once again failed to uphold its constitutional responsibility by refusing to block this unauthorized and dangerous war,” its senior policy adviser Cavan Kharrazian wrote.

The group also questioned why lawmakers did not hold a vote last week, after Trump threatened widespread destruction in Iran shortly before the ceasefire was announced. The president had written at the time on social media, “A whole civilization will die tonight.”

“We urge members of Congress, Democrats and Republicans alike, to support sustained diplomatic efforts to resolve this conflict,” Kharrazian added.

“The American people overwhelmingly reject this war and want a diplomatic end to it.”