WASHINGTON — President Trump’s decision to pull back on a planned military strike against Iran has divided Republicans, pitting hawks who criticized his midoperation retreat against a noninterventionist wing that sided with most Democrats to praise it.
The rift highlights a longstanding debate in the Republican Party over national security that has played out inside Mr. Trump’s White House and in the halls of Congress, and has resurfaced as Iran’s bellicose actions have rekindled questions over lawmakers’ roles in matters of war and peace. It has also pointed up profound concerns among some Republicans, who are normally loath to criticize the president over such issues.
Representative Liz Cheney of Wyoming, the third-ranking House Republican, said on Friday that she was concerned about Mr. Trump’s restraint in response to the downing of an American drone, comparing it with President Barack Obama’s unfulfilled threat to strike Syria if it crossed a “red line” by using chemical weapons.
“Weakness is provocative,” she warned the radio host Hugh Hewitt. “A world in which response to attacks on American assets is to pull back or to accept the attack is a world in which America won’t be able to successfully defend our interests.”
Ms. Cheney, who has styled herself as a fierce attack dog on behalf of the Trump administration, wrapped her criticism in praise of the president, later telling reporters at the Capitol that he “has shown absolutely that he is going to stand up and do what’s right when it comes to defending the United States of America.”
But other Republicans said the episode raised questions about Mr. Trump’s decision-making on the gravest of issues. His assertion that he canceled the strike after hearing from military commanders that it could kill as many as 150 Iranians indicated a lack of preparedness, they said.
“The question is, were you not asking about casualties when you made the decision?” said Representative Adam Kinzinger of Illinois, a former Air Force pilot. “I would have much rather us not even start than do this. I’m all for a proportional response, and maybe that needed to be changed, but I don’t think this sends a great message.”
Mr. Kinzinger said he would wait to see whether Mr. Trump ultimately retaliated against Iran, but added, “If the response is no response, then I think this is a mistake of pretty big proportions.”
Representative Mike Gallagher, Republican of Wisconsin and a member of the Armed Services Committee, warned that without some sort of retaliatory move, the United States risked “a massive deterrence failure in the region, and it will only embolden Iran.”
“Simply saying we are going to do something and then not doing it, to me, then you’re in no man’s land,” Mr. Gallagher added. “That’s where Obama lived for eight years, and it’s a bad place to be.”
At the same time, many Republicans who share Mr. Trump’s often-stated distaste for foreign military entanglements praised the aborted strike as the best possible outcome.
“I am grateful that the president is not eager to lurch into another Middle Eastern regime change, in an endless, unfocused, unconstitutional way,” said Representative Matt Gaetz, Republican of Florida. “President Trump ran as a very different kind of Republican, someone who wanted to end wars, not start them.”
Democrats, too, were uncharacteristically complimentary, although Speaker Nancy Pelosi noted that she had not been informed of the planned strike in advance, a “departure” from past practice, and said any such action must be authorized by Congress.
“A strike of that amount of collateral damage would be very provocative, and I’m glad the president did not take that,” Ms. Pelosi told reporters. “We think there are many options that are not what they call kinetic — that is to say, a strike on the country — that might be more useful.”
A bipartisan group of senators — including Democrats like Tom Udall of New Mexico and Tim Kaine of Virginia and Republicans like Rand Paul of Kentucky and Mike Lee of Utah — plans next week to try to attach an amendment to a sweeping defense bill that would block funding for any military operations against Iran without explicit authorization from Congress.
Representative Adam B. Schiff of California, the chairman of the Intelligence Committee, said Mr. Trump should not be criticized for holding off on military action.
“I don’t think that people s