WASHINGTON — President Trump, who once called Defense Secretary Jim Mattis “one of the most effective generals that we’ve had in many, many decades,” has now affixed a more ominous label to the retired four-star Marine general: “Democrat.”

In a “60 Minutes” interview broadcast on CBS on Sunday night, Mr. Trump grouped his own defense secretary in with the political party that the president now describes at every turn as “an angry, left-wing mob” bent on destroying the country.

“I think he’s sort of a Democrat, if you want to know the truth,” Mr. Trump said.

But the president added that he did not know whether Mr. Mattis would be the next major departure from his administration, following the abrupt resignation announcement last week by Nikki R. Haley, the United States ambassador to the United Nations, and the expected exit this fall of Donald F. McGahn II, the White House counsel.

“He may leave,” Mr. Trump said of Mr. Mattis, though he called him “a good guy” and insisted that the two men still had “a very good relationship.”