Lawmakers are due to vote on a bipartisan resolution led by Republican Thomas Massie and Democrat Ro Khanna that would require Trump to obtain congressional authorization before continuing military operations against Tehran.

But the measure is widely expected to fail, a day after the Senate rejected a similar effort, underscoring Congress's limited appetite -- particularly among Republicans -- for confronting the White House in the early days of the conflict.

Even if it were to pass, Trump could veto it -- a step that would require two-thirds majorities in both chambers to override, an almost impossible threshold in the current Congress.

The vote comes less than a week after the United States and Israel began a sweeping military campaign against Iran, targeting missile facilities, naval assets and other infrastructure.

The strikes have already killed senior Iranian leaders, including Supreme Leader Ayatollah Ali Khamenei, and triggered retaliatory attacks across the region.

The conflict has also claimed American lives: six US servicemembers have been killed in retaliatory strikes, including on a US base in Kuwait, intensifying pressure on lawmakers to weigh in on a war that Congress has not explicitly authorized.

Democrats argue the administration has offered shifting explanations for the strikes and has failed to demonstrate that Iran posed an imminent threat requiring immediate military action.

- 'War of choice' -

"Donald Trump intentionally refused to get authorization from Congress for this war of choice, a war that has now exploded to more than 10 countries across the Middle East," House Democratic Minority Leader Hakeem Jeffries said.

Under the Constitution, only Congress has the power to declare war. The 1973 War Powers Resolution -- passed after the Vietnam War -- was intended to prevent presidents from committing US forces to prolonged conflicts without congressional consent.

The House resolution invokes that law, directing the president to withdraw US forces from "unauthorized hostilities" involving Iran unless lawmakers explicitly approve the operation.

But Republican leaders have rallied behind Trump, arguing that limiting his authority during an ongoing military campaign would embolden Iran and endanger US troops.

"I think passage of a war powers resolution right now would be a terrible, dangerous idea...It would empower our enemies, House Republican Speaker Mike Johnson told reporters.

"It would kneecap our own forces, and it would take the ability of the US military and the commander in chief away in completing this critical mission to keep everybody safe."

Johnson urged Republicans to oppose the House measure, arguing that the military operation had been "limited, precise and extremely lethal," as well as a "remarkable success."

But Massie, one of the few Republicans willing to break with the administration, said Congress must reassert its constitutional role.

"Under our Constitution, the power to initiate war rests solely with Congress," he said. "Congress owes our service members a clearly defined mission, so that when they accomplish it, they can come home."