The defense secretary played down suggestions he was on the outs with President Trump, who recently said of Mr. Mattis, “I think he’s sort of a Democrat.”
HO CHI MINH CITY, Vietnam — Defense Secretary Jim Mattis played down suggestions that he was in danger of losing his job, as he made a case for leaving the American military out of politics and asserting that the country’s sharp divisions have no place among either the men and women who serve or the officers who lead them.
One day after President Trump suggested that Mr. Mattis is a Democrat — an accusation that in past Republican administrations wouldn’t mean much but in this one is close to treason — the retired four-star Marine general brandished bipartisan support for the American military in Congress as a point of pride, not shame.
“When I was 18, I joined the Marine Corps, and in the U. S. military we are proudly apolitical,” Mr. Mattis told reporters aboard a 20-hour flight to Ho Chi Minh City, Vietnam, from Washington. “By that, I mean that in our duties, we were brought up to obey the elected commander in chief, whoever that is.”
He said that he had not registered as either a Democrat or a Republican and sought to dismiss reports that his relationship with Mr. Trump has soured in recent months.
But those reports were only amplified on Sunday when CBS broadcast a “60 Minutes” interview with Mr. Trump in which the president said that Mr. Mattis “may leave” and “I think he’s sort of a Democrat, if you want to know the truth” — fighting words in a month when the president has accused Democrats of being an “angry, left-wing mob” bent on destroying the country.
Mr. Mattis said he had not watched the interview. “I’m on his team,” he said. “We have never talked about me leaving.”
Two hours later, Mr. Mattis reappeared before reporters to say that the president had just called him from Air Force One to reassure him that he was “100 percent” behind his defense secretary.
But administration officials said that Mr. Trump’s comments on “60 Minutes” reflected the president’s distaste for the very bipartisanship and political neutrality that Mr. Mattis constantly espouses. Mr. Trump doesn’t want that, aides say.
Rather, the president wants public loyalty and political support from his cabinet. Mr. Mattis’s belief that the American military should be above the political fray clashes with the president’s view that the military and its generals belong to him, one administration official said.
And even if Mr. Mattis is not a registered Democrat, he is viewed more warmly by Democrats than any other member of the Trump administration. Mr. Mattis famously clashed with President Barack Obama over Iran policy when he was the head of United States Central Command, but he had a good relationship with Hillary Clinton and was viewed by many as a likely candidate for defense secretary had she won the 2016 presidential election.
She didn’t, and he became defense secretary anyway, initially embraced by Mr. Trump, whom Mr. Mattis only met for the first time at his job interview during the transition. The two men got off to a great start, with Mr. Mattis talking Mr. Trump out of torturing detainees and advocating on behalf of American alliances around the world.
But in recent months, strains have started to show, in part because, aides say, Mr. Trump has come to resent the narrative of Mr. Mattis as the only adult in the room in a chaotic White House.
What’s more, the decision by John R. Bolton, the national security adviser, to appoint Mira Ricardel as his deputy was viewed by many at the Pentagon as a direct affront to Mr. Mattis, who clashed with Ms. Ricardel when she served as a Pentagon transition official for the new administration.
The president’s decision to publicly air differences with his defense secretary is bound to make Mr. Mattis’s job even tougher, especially as he goes about the business — as he is doing this week — of trying to represent the Trump administration on the world stage.
Mr. Mattis pointed to his trip to Vietnam, where he will be seeking to clear up some of the last remaining issues of the Vietnam War, and Singapore, where he will be meeting with Asian defense ministers, as proof that he remains part of Mr. Trump’s national security team.
“You can see right here, we’re on our way, we just continue doing our job,” he said.
But the counterparts he will be meeting here may have questions of their own about whether the defense secretary is on the same page as his boss. The fact is that Mr. Trump has the final say on a wide range of issues, from how to handle the deteriorating relationship with China, which Mr. Mattis is trying to mend, to whether the United States should continue to suspend military exercises in the Korean Peninsula as a sweetener to North Korea, a concession that Mr. Mattis opposed.
While the president also gets to decide the makeup of his cabinet, any decision by Mr. Trump to fire Mr. Mattis would very likely stir up bipartisan trouble with Congress.
Asked last month about reports that Mr. Trump was thinking of getting rid of Mr. Mattis after the midterm elections, Representative Mac Thornberry, the Texas Republican who heads the House Armed Services Committee, said he was against the idea.
“I think he is a great secretary of defense who has tremendous credibility on Capitol Hill, around the world,” Mr. Thornberry said. “I would do everything I could to keep him there as long as possible.”
