Republican presidential candidate Newt Gingrich said fellow candidate Mitt Romney was being stubborn tonight when Gingrich appeared on "The Situation Room with Wolf Blitzer."

Gingrich was asked about changing his position on health mandates. He admitted he had changed his position, but said supported health mandates in the past to block Hillary Clinton's failed health care proposals because he thought mandates would be less damaging. Gingrich called supporting mandates a mistake.

Blitzer asked Gingrich if Romney is wrong for standing by his health care policies in Massachusetts.

"Yeah," Gingrich said, "and I think he was wrong. I think the difference between Mitt and I is that I think I was wrong and I changed. I think down deep he thinks he's been wrong but he's being stubborn."

Today, the Romney campaign released an advertisement that noted Romney has been married for 42 years and has belonged to the same church his entire life. Some in the media, including Blitzer, suggested the ad could be a dig at Gingrich's turbulent personal past.

Gingrich has been divorced twice and changed religions several times, converting to Catholicism only a few years ago. The Romney campaign did not respond to a request for comment on the ad.

"Look, I think Mitt Romney is a very admirable person and I'm not going to pick a fight over Mitt Romney," Gingrich said.

Gingrich said Romney and his wife, Ann Romney, are "terrific people" and have a "wonderful family." He added that his wife, Callista, recently signed copies of her children's book, "Sweet Land of Liberty," to Romney's grandchildren.

Gingrich said if he got the nomination, "there are circumstances" where Romney might be on his list of potential running mates.

"I don't know whether he would want to or not, but he's a very competent person. This is a serious man," Gingrich said. "I could certainly support him if he became the Republican nominee."

Gingrich is leading Romney in several Iowa Caucus-focused and national polls. Both candidates will participate in an ABC News debate on Saturday at 9 p.m. ET.