WASHINGTON - President Donald Trump assailed his former Secretary of State Rex Tillerson as "dumb as a rock" after Tillerson said in an interview Thursday that some of the president's ideas violated the law.

The president's harsh response included calling Tillerson "lazy as hell" and saying that Tillerson didn't "have the mental capacity needed" to do his job properly. That all has changed, Trump said, with Mike Pompeo, who took over the role after Tillerson's ouster.

"He was dumb as a rock and I couldn’t get rid of him fast enough," Trump said of his former top diplomat in a tweet Friday. "He was lazy as hell. Now it is a whole new ballgame, great spirit at State!"

Trump's comments came in response to an interview Tillerson gave with CBS News. He said his time working for Trump was "challenging," calling his former boss "undisciplined" and saying that he'd have to tell the president that actions he wanted to take "violates the law."

"He acts on his instincts," Tillerson said Thursday, per an excerpt released by CBS News. "In some respects, that looks like impulsiveness. But it's not his intent to act on impulse. I think he really is trying to act on his instincts."

Trump’s former top diplomat made the comment during a talk with Bob Schieffer of CBS News at a fundraiser in Houston.

He continued: "It was challenging for me, coming from the disciplined, highly process-oriented Exxon Mobil Corporation, to go to work for a man who is pretty undisciplined, doesn't like to read, doesn't read briefing reports, doesn't like to get into the details of a lot things."

Tillerson served as secretary of state for more than a year before being abruptly fired by Trump in March.

Asked by Schieffer how his relationship with the president "went off the rails," Tillerson said that he and Trump had "starkly different" styles and that Trump would become frustrated when Tillerson told him that something he wanted to do would violate the law or a treaty.

"We did not have a common value system," Tillerson said. "When the president would say, ‘Well here’s what I want to do. And here’s how I want to do it.’ And I’d have to say to him: ‘Well, Mr. President, I understand what you want to do but you can’t do it that way. It violates the law, it violates a treaty.’ You know. He got really frustrated.

"I didn’t know how to conduct my affairs with him any other way than in a very straightforward fashion," Tillerson said. "And I think he grew tired of me being the guy every day that told him, “You can’t do. And let’s talk about what we can do.’"

On Thursday, Tillerson also doubled down his previous assertions about Russian interference in the 2016 election.

"There’s no question" that Russia meddled, he said, adding that the interference was well-documented within intelligence agencies, according to the Houston Chronicle.

“What Russia wants to do is undermine our confidence and undermine the world’s confidence in us,” Tillerson said.

More: Mueller, Cohen, Manafort: This is why Friday is expected to be filled with political news

Related: As major developments loom, President Trump again goes after special counsel Robert Mueller

Tillerson’s comments came one day before major news is expected to break Friday on Special Counsel Robert Mueller’s Russia investigation.

The updates in the Russia investigation include prosecutors explaining why a plea agreement with Paul Manafort, Trump's former campaign chairman, fell apart, and a sentencing memorandum that could outline what Michael Cohen, the president's former attorney, told investigators.

Contributing: Christal Hayes