The Pentagon downplayed President Trump's speculation regarding Defense Secretary Jim Mattis' personal politics and future in the administration, saying Sunday the retired four-star general was preoccupied with issues of national security.

"Secretary Mattis is laser-focused on doing his job — ensuring the US military remains the most lethal force on the planet," Col. Rob Manning, a Department of Defense spokesman, told the Washington Examiner in a short statement.

Trump told CBS News in an interview set to air Sunday night on "60 Minutes" that Mattis was "sort of a Democrat" when asked about the secretary's future in the president's Cabinet. Trump's comments were made in the context of questions probing the high staff turnover he has experienced during the first 18 months of his time in office.

"I think he's sort of a Democrat, if you wanna know the truth," Trump said of Mattis, who has served Republican and Democratic presidents and is not required to disclose his party affiliation as a registered voter in Washington state. "But Gen. Mattis is a good guy. We get along very well. He may leave. I mean, at some point, everybody leaves. Everybody. People leave. That's Washington."

While Mattis had not signaled to Trump that he had any intention of stepping down from his post at the Pentagon, the president said to expect more changes within his administration.

"Yeah, other people will go, sure," Trump said. "I think I have a great Cabinet. There's some people that I'm not happy with. I have some people that I'm not thrilled with. And I have other people that I'm beyond thrilled with."

[More: Trump: 'I know more' about NATO than Defense Secretary Jim Mattis]