President Donald Trump will remain in office for eight years, and the thought of that "horrifies liberals," former House Speaker Newt Gingrich said Tuesday.

"Mayor [Michael] Bloomberg said the other day," Gingrich, the author the new book "Understanding Trump," told "CBS This Morning."

"It horrifies liberals. I think he'll be there for eight years. The power of a president to survive is unbelievable."

Trump, he continued, is learning "every day a little bit" more.

"Look at his foreign trip, which was a tour de force," said Gingrich, rejecting a comment from a CBS interviewer that the European portion of the president's trip through the Middle East and Europe was "not good."

"The European part, he accomplished what he intended," Gingrich said, agreeing that the presidency is a work in progress that "will be until the day [Trump] leaves.'

Gingrich also discussed Attorney General Jeff Sessions' upcoming Senate testimony, and said that he believes he will be more forthcoming about his meetings with Russian Ambassador Sergey Kislyak.

"His answer was that he misunderstood the question," said Gingrich, and he believes that to be true.

"Originally [they asked] him, 'have you met with Russians in your campaign role?' said Gingrich. "He said no. He met with them twice as a U.S. senator. It turn out all sorts of U.S. senators routinely meet with the Russian ambassador. It's a courtesy."

During his testimony before the Senate Intelligence Committee last Thursday, former FBI Director James Comey said Sessions may have met for a third, undisclosed time, with Kislyak, but Gingrich said there is doubt about that assertion.

"I think you'll find in this latest allegation that the Russian ambassador was one of 90 people in a room, and then he rode home and said 'I met with Senator Sessions because it made him look good,'" said Gingrich.

"There's no evidence they ever met except maybe walking through the Mayflower [Hotel] at a reception."

The news is all based on hearsay, continued Gingrich, and "based on an intercept of the Russian ambassador saying I met with him."

"Pictures of the actual reception don't show the Russian ambassador anywhere near Sessions and Sessions is milling around with 90 people and there's no evidence there was a private meeting," said Gingrich.

He said he also does not believe Trump is considering firing special counsel Robert Mueller, despite reports surfacing Monday saying that he plans to.

"I think the president is pretty confident that this is all going to come out in the wash and ultimately, he's still going to be president and this stuff is going to go away," said Gingrich.

"I think the president, I know because we've talked about it."

That conversation occurred Monday night, said Gingrich.

"He called me because I've been very clear about the fact that Mueller, hiring four Democrats — the attorneys are all Democrats, one of them worked for the Clinton Foundation," said Gingrich.

"He couldn't find a single pro-Trump attorney to hire, I think that's a mistake to pretend that this is some neutral investigation."