Smith said that Gingrich's past marital infidelities should be left in the past since he'd apologized for them.

"He's made a point of saying 'look, I've made mistakes, I've tried to bring myself before God and say I'm sorry, I've made these mistakes,' and I believe in redemption, that's good enough for me," Smith said.

Gingrich's third wife, Callista, has had a "tremendous" impact on him, Smith argued.

"The man is a different man. She's very much his partner," he said. "People want to look back and say 'This is what it was 25, 30 years ago.' How do you stop that? You can only do what you can do, you can't change what you did."