Newt Gingrich joined Bill O'Reilly on "The Factor" to weigh in on how Republican candidates are faring in the 2016 race.

Gingrich said that he does not believe that current front-runner Donald Trump has peaked.

"I think this guy learns every day, I think he has endless amounts of energy. He has tapped into something real about the American people: The desire to to be great again, the desire to win," Gingrich said.

He noted that Trump has done much better than anyone predicted for about four months now, and he's adding more staff and organization to his campaign.

"He will be formidable. I do not think he will implode," Gingrich said. "Somebody will have to beat him to stop him from becoming the nominee."

Gingrich said that Dr. Ben Carson, who's second in many polls, is an even more remarkable figure than Trump.

"There's something magic happening with him. And I think people who are sick and tired of Washington, but also sort of tired of noise, have found in Dr. Carson the alternative to Trump," Gingrich said. "It's an amazing performance."

Watch the clip above to hear Gingrich's thoughts on other GOP candidates like Jeb Bush, Ted Cruz, Marco Rubio, Carly Fiorina and John Kasich.