“My investments are not made by me. My investments for the last 10 years have been in a blind trust, managed by a trustee,” Romney said.

Only Paul answered the question clearly: He would get the government out of the mortgage business. Paul differed from the other candidates in calling for fewer Cuba trade restrictions. The other candidates also have a more Israel-centric foreign policy.

Gingrich differed from the other candidates by calling for more space-travel — something Romney called “a big idea. But it’s a bad idea.”

Santorum lamented that Gingrich and Romney were playing “petty personal politics.”

But campaigns can hinge on pettiness and criticisms.

Romney is winning that war, just as he did in Iowa when Gingrich was surging there. Not only is he out-advertising Gingrich, cable-news networks and some news outlets that picked up a Romney line from a previous debate and questioned whether the former House Speaker was really close to Reagan.

Gingrich blamed “the Romney attack machine.” On the campaign trail, Gingrich acknowledged it has taken a toll. He sounded weary.

Gingrich also criticized Romney for living “in a world of Swiss bank and Cayman Island bank accounts." Blitzer asked about it. Gingrich called it a “nonsense” question.

But unlike last week’s South Carolina debate, where Gingrich turned the tables on the CNN moderator, Blitzer didn’t back down.

“I didn’t say that,” Blitzer said. “You did.”

Santorum, too, got his shots in — but on Romney. He pointed out that Romney’s healthcare plan in Massachusetts mirrored President Barack Obama’s. It was a major issue in 2010.

Romney tried to explain the differences. But Santorum pointed out that people in Massachusetts now need to buy health insurance — just like “ObamaCare mandates.”

“Folks, we can’t give this issue away in this election,” Santorum said. “It is about fundamental freedom.”

Santorum will likely lose Tuesday, but his picking apart of Romney’s healthcare plan was a pitch-perfect echo of conservative worries about Romney’s candidacy.

In that respect, Obama won this part of the debate without saying a word.