And it suggested that when it comes to the president’s strategy in Iran, there are at least some cracks in Republican support, as administration officials continue to offer few details on the intelligence that led them to authorize the killing of General Suleimani.
Since arriving in the Senate in 2011, Mr. Lee has been an outspoken backer of attempts to reclaim Congress’s authority, particularly around issues of war and peace. One of the founders of the Article One Project, an initiative intended specifically to enable “congressional rehabilitation,” Mr. Lee broke party ranks last year to join Democrats in leading a war powers resolution directing Mr. Trump to cut off military aid to Saudi Arabia’s campaign in Yemen.
Wednesday’s briefing, he said, inspired him to again defect from his party and support a war powers resolution led by Senator Tim Kaine, Democrat of Virginia, that would limit Mr. Trump’s war powers on Iran. Mr. Lee said he was initially unsure whether he would support the measure, citing some qualms with the wording of the legislation.
“I can say that after that briefing — that briefing is what changed my mind,” he said.
Almost all of Mr. Lee’s Republican colleagues appeared to disagree on Wednesday. Senator Jim Risch of Idaho, the chairman of the Foreign Relations Committee, told reporters it was “one of the best briefings” he had ever attended, calling the information the officials relayed “crystal clear.”
But Senator Rand Paul, Republican of Kentucky, another libertarian who has worked to insist on congressional war powers, said he agreed with Mr. Lee and would also support Mr. Kaine’s resolution.
“Today, this is Senator Lee and I saying we are not abdicating our duty,” Mr. Paul said.
The development was potentially significant, since a War Powers Resolution needs only 51 votes to pass. Republicans control 53 votes in the Senate and Democrats 47, though it is unclear whether all Democrats would support such a measure.
Mr. Lee’s remarks were lauded by Democrats, who have criticized the administration’s briefings and notifications to Congress.