CONCORD, N.H. -- Mitt Romney found himself under fire early in a Sunday GOP debate, with conservative candidates piling on Romney's record as governor of Massachusetts.

Former House Speaker Newt Gingrich and former Pennsylvania Sen. Rick Santorum went on the attack at the outset of Sunday's NBC News-Facebook debate, broadcast on "Meet the Press." The two of them went after Romney from his right flank, assailing him as an inauthentic conservative.

"If his record was so great as governor of Massachusetts, why didn't he run for reelection?" asked Santorum, the candidate who basically tied Romney in last Tuesday's Iowa caucuses. "If it was so great, why did you bail out?"

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The offensive against Romney were an element largely absent from another GOP debate last night in Manchester. The rest of the Republican field is looking to draw distinctions with Romney in the remaining 48 hours before the New Hampshire primary, in which Romney is leading, according to polls.

"I'm very proud of my record and I think the one thing you can't fool the people of New Hampshire about is the record of a governor next door," Romney said in response to the pile-on, largely avoiding making direct attacks against his detractors.

At one point, though, when Santorum interrupted him, Romney snipped: "Rick, it's still my time."

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Gingrich, who had vowed to draw more stark contrasts against Romney in New Hampshire after having been assailed by ads in Iowa run by a pro-Romney super PAC, voiced criticisms of Romney similar to the ones he'd voiced while barnstorming through the Granite State this week.

"I think that a bold Reagan conservative, with a very strong economic plan, is a lot more likely to succeed in that campaign than a relatively timid, Massachusetts moderate who even the Wall Street Journal said had an economic plan so timid it resembled Obama," Gingrich said.

But the former speaker also said that he didn't think that Romney was unelectable -- differing from the language contained in a flier distributed by the Gingrich campaign calling Romney "not electable."

In one of the morning's undercard battles, Santorum and Texas Rep. Ron Paul sparred over the libertarian congressman's scant record of legislative accomplishments, and Paul's foreign policy favoring more limited international involvement.

"The problem with Congressman Paul is that all the things Republicans like about him he can't accomplish, and all the things they don't want him to do, he can do day one," Santorum said.

Paul has drawn boisterous crowds in just a handful of rallies here in New Hampshire. But he ranks second, at 22 percent, in this week's NBC News-Marist poll of likely GOP primary voters in the state.

He defended his legislative record as evidence that it's Congress that's out-of-touch.

"That demonstrates how out of touch the U.S. government and the U.S. Congress is with the American people," he said.

The gathering represented another chance for candidates to draw contrasts with each other after a Saturday night debate did little to alter the trajectory of the campaign. Former Massachusetts Gov. Mitt Romney, who leads handily in polling of this week's primary, went relatively unscathed in the debate.

New Hampshire voters head to the polls on Tuesday to vote in the nation's first primary of the 2012 cycle, and the second nominating contest following last Tuesday's Iowa caucus. Romney battled Rick Santorum to a virtual draw in the Hawkeye State, earning an 8-vote victory over the former Pennsylvania senator.

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