WASHINGTON — Speaker Nancy Pelosi announced on Wednesday that the House would vote on Thursday to force President Trump to quickly wind down military action against Iran unless he is given explicit authorization from Congress, opening what promised to be a searing debate over presidential war powers.
Ms. Pelosi issued the statement as lawmakers breathed a sigh of relief on Capitol Hill after Mr. Trump said he would back away from any military escalation against Tehran. But congressional Democrats, skeptical of the administration’s case for the drone strike last week that killed Maj. Gen. Qassim Suleimani and dissatisfied with the rationale Mr. Trump’s team offered for conducting it, pledged to press ahead with their efforts to rein in the president’s war-making authority.
They said the vote on Thursday would be on a measure that would require that Mr. Trump cease all military action against Iran unless Congress votes to approve it. Such a measure could face an uphill climb in the Republican-controlled Senate, but on Wednesday, two Republicans signaled they were inclined to support it, holding open the possibility of a razor-thin vote. Either way, it is certain to ignite a fierce debate over Mr. Trump’s strategy on Iran, and Congress’s role in curtailing a president’s ability to wage war.
“Members of Congress have serious, urgent concerns about the administration’s decision to engage in hostilities against Iran and about its lack of strategy moving forward,” Ms. Pelosi said in a statement. “Our concerns were not addressed by the president’s insufficient War Powers Act notification and by the administration’s briefing today.”
The day after Iranian missile struck bases in Iraq where American troops are stationed, Republicans and Democrats in Congress split sharply over the president’s approach on Iran and the way forward. Amid back-to-back classified briefings by top administration officials for members of the House and Senate, most Republicans praised Mr. Trump effusively on Wednesday for targeting General Suleimani and for his restraint in responding to Iran’s action.
Senator Mitch McConnell, Republican of Kentucky and the majority leader, said the president had shown “patience and prudence.”
“As a superpower, we have the capacity to exercise restraint and to respond at a time and place of our choosing, if need be,” he said. “I believe the president wants to avoid conflict or needless loss of life. But he’s rightly prepared to protect American lives and interests.”
But a couple of Republicans joined Democrats in raising grave questions about Mr. Trump’s strategy, concerns that only sharpened after the briefings on Capitol Hill by Secretary of State Mike Pompeo, Defense Secretary Mark T. Esper, and the C.I.A. director, Gina Haspel.
Senators Mike Lee of Utah and Rand Paul of Kentucky, who have long been vocal proponents of asserting Congress’s war-making authority, said they would back a Senate version of the House Democrats’ resolution because they found the administration’s presentation to be so “insulting.”
The message from the administration, Mr. Lee said, was “to run along and be good little boys and girls and not debate” the justification for the strike that killed General Suleimani. “It’s un-American, it’s unconstitutional, and it’s wrong,” he said.
The pair’s defections could be significant in the Senate, where Republicans control 53 votes to Democrats’ 47, and only 51 are needed to approve a resolution concerning war powers.
Democrats voiced their own serious doubts about the president’s actions and what they called the dearth of credible information from the administration about his strategy on Iran. The Iranian attacks had only strengthened their resolve to reassert Congress’s role in matters of war, they said.
Representative Gerald E. Connolly, Democrat of Virginia, described the briefing as “sophomoric and utterly unconvincing.”
“I believe more than ever the Congress needs to act to protect the constitutional provisions about war and peace,” he told reporters, adding, “I believe there was no rationale that could pass a graduate school thesis test.”
Appearing on MSNBC on Wednesday, Senator Sherrod Brown, Democrat of Ohio, also expressed skepticism.
During the briefing, he said, he “heard the same kind of lies I was hearing 20 years ago when I was a member of the House on the war in Iraq.”
Warning of the possible consequences, Ms. Pelosi noted, “America and the world cannot afford war.”
Democrats were still debating Wednesday evening how quickly to move on limiting Mr. Trump’s war powers. The Senate measure, sponsored by Senator Tim Kaine of Virginia, gives the president a 30-day deadline to come to Congress for authorization for military action, and Ms. Pelosi told Democrats on Sunday that the House would consider a resolution with the same timetable. But a draft of the proposal released on Wednesday did not specify a deadline.
Ms. Pelosi said that the House may also vote on a pair of measures to further constrain Mr. Trump’s war powers that Democrats included this year in the annual defense policy bill, but were ultimately stripped out before its final passage. One, led by Representative Ro Khanna of California, would bar the president from using funds provided by Congress to strike Iran without lawmakers’ permission. The other, led by Representative Barbara Lee of California, would repeal a 2002 measure granting President George W. Bush authorization to use military force in Iraq.
It is that authorization, along with the president’s power as commander in chief to defend United States forces against imminent threats, that the Trump administration has cited as justification for having targeted General Suleimani.
In the briefings to Congress on Wednesday, Democrats pressed administration officials on the use of the 2002 authorization for the strike, and left the closed-door presentations saying the answers had been woefully deficient.
“The administration has not offered a remotely sufficient justification for the legal basis of this action,” said Representative Jamie Raskin, Democrat of Maryland.
But Senator Marco Rubio, Republican of Florida, said the administration had ample authority to order the strike, adding that officials provided “clear intelligence” that there was not only an imminent threat to United States forces, but also an “ongoing near-term threat.”
“We never need congressional authority in this country to act in the defense of our troops, and that’s what this administration has done,” Mr. Rubio said. “They have been very clear they don’t seek to start a war, and if there is military action, it will be in response to Iranian proxy actions, not because we started it first.”
Michael D. Shear and Emily Cochrane contributed reporting.