Mitt Romney's rivals for the US Republican presidential nomination slammed his "pious baloney" on the campaign trail and tarred him as a timid moderate sure to lose to Barack Obama.
Squaring off in their second televised debate in just 10 hours, the other contenders seemed determined to seize what could be a final chance to dull Mr 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 Mr 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" in the 6 November elections, said Mr Gingrich.
"I'm very proud of the conservative record I have," replied Mr Romney, who is seen as the likely nominee if he can make good on his vast lead in opinion polls here and in South Carolina after eking out a win in the Iowa caucuses last week.
In a shot at Mr Gingrich and former senator Rick Santorum, a devout Christian conservative, Mr Romney said "someone who isn't a lifelong politician" would have a better shot at beating US President Obama and underlined "we've got to nominate a leader."
Mr Santorum pointed to Mr Romney's decision not to run for re-election as governor in the face of poor poll numbers and thundered:
"We want someone, when the time gets tough - and it will in this election - we want someone who's going to stand up and fight for the conservative principles, not bail out and not run."
"Politics is not a career. For me, my career was being in business," said Mr Romney, who made millions as a venture capitalist and mounted a failed bid for the party's nomination in 2008.
"Can we drop a bit of the pious baloney?" Mr Gingrich scolded in an exasperated tone. "You were running for president while you were governor... you've been running consistently for years and years and years."
While the attacks amounted to a sharp escalation in tone against Mr Romney, he gave as good as he got and committed no major errors, making it unlikely that the assault would derail his better-funded, better-organized campaign.
Still, 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 Mr Romney and successive conservatives who have surged and fallen back.
Mr 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%.
And a New Hampshire tracking poll from Suffolk University in nearby Boston could breath fresh life into his rivals: It found his standing in his state slipping for the fourth straight day, though still enjoying a wide lead.
The survey gave Mr Romney 35% support, down from 43% last Tuesday, well above Ron Paul's second-place 20%, while former US envoy to China Jon Huntsman gained to 11%, and Mr Gingrich sits at 9%.
The poll found Mr Santorum has fallen to 8% - a slide pollsters have blamed on his virulent criticisms of gay rights in independent-minded New Hampshire - while Rick Perry was at 1%.
The former senator - who has likened being gay to bestiality - stuck by his fierce opposition to gay marriage and gay adoptions but struck a far softer personal tone when asked what he would do if he had a son tell him he was gay.
"I would love him as much as I did the second before he said it. And I would try to do everything I can to be as good a father to him as possible," said Mr Santorum.
Mr Romney said he - like Mr Obama - opposes same-sex marriage but warned that voters seeking a candidate who would deny gays "full rights in this country" that "they won't find that in me."
Polls have shown the US public increasingly supportive of gay rights - especially among the young.
Mr Huntsman scored one of the biggest applause-getting lines of the debate when he rebuked Mr Romney for attacking his service as Mr Obama's first ambassador to China, saying he was "putting my country first."
Mr Romney retaliated, saying "the person who should represent our party running against President Obama is not someone who called him a remarkable leader and went to be his ambassador in China."
However Mr Huntsman won more applause when he shot back to NBC moderator David Gregory: "This nation is divided, David, because of attitudes like that. The American people are tired of the partisan division. They have had enough."
