Frontrunner Mitt Romney's rivals for the Republican presidential nomination have slammed him as a 'timid' moderate who will lose the November election to President Barack Obama.
Squaring off in their second televised debate in 10 hours, the other contenders seemed determined to seize what could be a final chance to dull Romney's momentum days before New Hampshire's bellwether primary on Tuesday.
Former House speaker Newt Gingrich accused the former Massachusetts governor of being a "moderate" with "an economic plan so timid it resembles Obama's" and warned Republicans against thinking Romney is the most electable candidate.
"I do think the bigger the contrast, the bolder ideas, the clearer the choice, the harder it is for that billion-dollar campaign to smear his way back into office," Gingrich said on Sunday.
"I'm very proud of the conservative record I have," replied Romney, who is seen as the likely nominee if he can make good on his vast lead in opinion polls in New Hampshire and in South Carolina after eking out a win in the Iowa caucuses last week.
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In a shot at Gingrich and former senator Rick Santorum, a devout Christian conservative, Romney said "someone who isn't a lifelong politician" would have a better shot at beating Obama and underlined "we've got to nominate a leader".
Santorum pointed to Romney's decision not to run for re-election as governor in the face of poor standings in the polls, saying conservatives "want someone who's going to stand up" and won't "bail out and run".
"Politics is not a career. For me, my career was being in business," said Romney, who made millions as a venture capitalist.
"Drop a bit of the pious baloney," said Gingrich. "You were running for president while you were governor ... you've been running consistently for years and years and years."
The debates could shape Tuesday's vote, which may drive one or more candidates from the race, resetting a field that has been led alternately by Romney and successive conservatives who have surged and fallen back.
Romney's vast campaign war chest and high-profile endorsements have fed his image as the candidate to beat, but he faces stubborn doubts about his conservative credentials and has never been able to push his support from Republicans nationwide above 30 per cent.
