WASHINGTON – President Donald Trump described his defense secretary as "sort of a Democrat" and said he may leave the administration after the midterm elections in an interview airing on "60 Minutes" Sunday.

"He may leave," Trump said of Defense Secretary Jim Mattis, according to an interview excerpt released by CBS News. "I mean, at some point, everybody leaves. Everybody. People leave. That's Washington."

The New York Times reported last month that Trump may have soured on Mattis. In addition to thinking that Mattis is a Democrat at heart, The Times said, Trump doesn't like being unfavorably compared to Mattis.

For his part, the defense secretary has said Trump acts as if he has the understanding of a fifth- or sixth-grader, according to Washington Post reporter Bob Woodward's recently published book "Fear."

Asked if he wants Mattis gone, Trump told 60 Minutes that he has a "very good relationship" with the defense secretary, whom he called a "good guy."

But, Trump said, "it could be" that Mattis is leaving.

"I think he's sort of a Democrat, if you want to know the truth," Trump said.

After his first year in office, Trump's administration already had the highest rate of turnover among White House staff in decades, according to the Brookings Institution.

The latest high-profile figure to announce her departure was Nikki Haley, Trump's ambassador to the United Nations, who is stepping down at the end of the year.