“He’s interfering with the chain of command, which is trying to police its own ranks,” said Peter D. Feaver, a specialist on civilian-military relations at Duke University and former aide to President George W. Bush. “They’re trying to clean up their act and in the middle of it the president parachutes in — and not from information from his own commanders but from news talking heads who are clearly gaming the system.”

Chris Shumake, a former sniper who served in Chief Gallagher’s platoon, said in an interview that he was troubled by the impact the president’s intervention could have on the SEALs.

“It’s blown up bigger than any of us could have ever expected, and turned into a national clown show that put a bad light on the teams,” said Mr. Shumake, speaking publicly for the first time. “He’s trying to show he has the troops’ backs, but he’s saying he doesn’t trust any of the troops or their leaders to make the right decisions.”

Chief Gallagher, who has denied any wrongdoing, declined through his lawyer to be interviewed. Mr. Trump’s allies said the president was standing up to political correctness that hamstrings the warriors the nation asks to defend it, as if war should be fought according to lawyerly rules.

“From the beginning, this was overzealous prosecutors who were not giving the benefit of the doubt to the trigger-pullers,” Pete Hegseth, a weekend host of “Fox & Friends” who has promoted Chief Gallagher to the president both on the telephone and on air, said this past week. “That’s what the president saw.”

‘No One Touch Him. He’s Mine.’

Chief Gallagher, 40, a seasoned operator with a deeply weathered face from eight combat deployments, sometimes went by the nickname Blade. He sought out the toughest assignments, where gunfire and blood were almost guaranteed. Months before deploying, he sent a text to the SEAL master chief making assignments, saying he was “down to go” to any spot, no matter how awful, so long as “there is for sure action and work to be done.”

“We don’t care about living conditions,” he added. “We just want to kill as many people as possible.”