When asked on "60 Minutes" if Mattis might leave the administration, Trump said he had "a very good relationship with him. It could be that he is. I think he's sort of a Democrat, if you wanna know the truth."
"But Gen. Mattis is a good guy," said Trump. "We get along very well. He may leave. I mean, at some point, everybody leaves. Everybody. People leave. That's Washington."
Mattis told reporters traveling with him to Vietnam that he and Trump had spoken on Monday while the president was en route to Florida.
In their first conversation since the 60 Minutes interview was taped, Mattis told reporters that Trump had told him, “I’m a hundred percent with you” and “I’m with you a hundred percent.”
Mattis' comments were a clarification of his earlier comments to reporters that he had not spoken with the president since the interview had aired on Sunday.
Asked earlier what he had thought about Trump's comments, Mattis told reporters "Nothing at all."
"I’m on his team," Mattis said. "We have never talked about me leaving. And as you can see right here, we're on our way. We just continue doing our job."
Mattis said he had not seen the interview with the President and only seen reporting about it in the press.
Reporters also asked Mattis if he had ever registered as either a Democrat or Republican.
"I’ve never registered for any political party," said Mattis, who is registered to vote in his home state of Washington, which does not require political affiliations to be disclosed.
When asked earlier if he was a Democrat, Mattis had replied with a lengthy statement that having served a lifetime in the U.S. military, "we are proudly apolitical."
"By that, I mean that in our duties, we were brought up to obey the elected commander in chief, whoever that is," said Mattis.
"Where am I today? I'm a member of the president's administration," said Mattis.
"You can see that my portfolio is bipartisan by its very basis, and that is the protection of the United States," he added.
"That's what President Trump has told me to do, and I eagerly carry that out, alongside probably the most selfless young men and women -- not all young; some old men and women, too -- civilian and military, Army, Navy, Air Force, Marines working together," he said. "So that's where I stand. That defines me."