“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.