Pushing back, Huckabee accused Romney of defensiveness when challenged.

"Somebody raises a question and you say it's a personal attack," Huckabee said. He added that he raised some taxes in response to a court order to improve education, then told Romney: "Maybe you don't have to obey the court in Massachusetts. I did in Arkansas."

Spilling into the fiscal debate was a fight over who can best change the country's direction. Bridling at Romney's description of him as a Washington insider, McCain said he had fought entrenched interests to save taxpayer money.

"Look, ask Jack Abramoff, who's in prison today, a guy who was a corrupt lobbyist and his friends, if I haven't cut spending," McCain said. "Ask the Air Force and Boeing, where I saved $2 billion -- $2 billion by fighting against a bogus Air Force tanker deal."

Tension arose again on immigration. Romney questioned Huckabee on allowing children of illegal immigrants in Arkansas to pay the same college tuition rates as state residents.

"Mitt, I'm talking to Chris right now, if you don't mind," Huckabee said, referring to moderator Chris Wallace.

"Well, that is actually a question I was going to ask," Wallace said.

"Well, you can ask it," Huckabee said, "but I've decided that you're the moderator of the debate, not Mitt, and he's tried to engage me in this."

Wallace set some of the collisions in motion. He asked Huckabee about his comment before the Iowa caucuses that Romney was running a "dishonest, desperate campaign."

That led to more back-and-forth that stretched from Romney recalling that Huckabee campaign Chairman Ed Rollins said he wanted to "kick my teeth in," to Huckabee mentioning that one of his celebrity supporters, Hollywood tough guy Chuck Norris, was outside.

"If John Wayne was here," Thompson quipped, "I'd have him beat [Norris] up."

When the subject turned to Romney's hard-edged ads, Huckabee called them "misleading." But Romney defended the ads.

"I do think that there's a difference between an attack ad, where people go after somebody based on their character, and describing someone's record," Romney said. "If people think their record or their positions is an attack ad, that's a strange thing."

Then he accused his rivals of attacking him. "Some of the ads that have come back, or some of the words that have come back, have been very different than just talking about issues," Romney said. "Sen. McCain's ad was pretty tough."