Even though the threat of further conflict with Iran appeared to recede for now, Speaker Nancy Pelosi announced that the House would vote on Thursday on a measure curtailing Mr. Trump’s war-making power by requiring him to halt military action against Iran within 30 days unless Congress votes to approve it.

Such a measure has little chance of becoming law given Republican control of the Senate and Mr. Trump’s veto pen, although Mr. Lee said he had been persuaded to vote for a similar resolution being offered by Senator Tim Kaine, Democrat of Virginia, because of the administration briefer’s effort to silence him.

Mr. Trump’s 10-minute televised statement on Wednesday morning was his most extended effort to explain last week’s drone strike on General Suleimani. He surrounded himself with his national security team, including Vice President Mike Pence, Secretary of State Mike Pompeo, Defense Secretary Mark T. Esper, General Milley and Robert C. O’Brien, the national security adviser. They stood stoically around the president without commenting.

The administration’s messages have been conflicting and confusing. In recent days, the president was forced to walk back threats to target Iranian cultural sites after the defense secretary made clear that doing so would be a war crime. The American headquarters in Baghdad had written a letter indicating it was withdrawing from Iraq, only to have the Defense Department say it was a draft document with no authority.

In his statement on Wednesday, Mr. Trump sought to pin the current crisis on a predecessor, blaming former President Barack Obama for striking a “foolish” nuclear agreement with Iran in 2015 that unfroze billions of dollars of money for Tehran that could be used to finance ballistic missiles and terrorist activity. “The missiles fired last night at us and our allies were paid for with the funds made available by the last administration,” Mr. Trump said.

There was no way to know if that was literally true, because money is fungible, but some of the president’s claims about the nuclear agreement were false, exaggerated or unsubstantiated claims. He asserted, among other things, that Iran’s hostile acts against America and its allies increased after the deal, rather than after the Trump administration withdrew from it in 2018, as statistics indicate.

Either way, he urged Britain, France, Germany, Russia and China to recognize that it was effectively dead and called on those countries to join him in negotiating a replacement for the Joint Comprehensive Plan of Action, as the agreement is officially known, that would go further to constrain Iran’s nuclear ambitions.