With only two full days left before the first-in-the-nation New Hampshire primary, Republican candidates faced off as former Gov. Mitt Romney, fighting for his political life, accused Sen. John McCain of supporting "amnesty" for illegal immigrants, and sparred with former Gov. Mike Huckabee over his criticism of Bush administration foreign policy.
Sparks flew quickly in the debate, hosted by ABC News, Facebook and WMUR, the local ABC affiliate station.
Touching off a heated exchange between Huckabee and Romney, moderator Charles Gibson asked the Republican rivals, who sat in a semi-circle on a stage at St. Anslem's College in Manchester, N.H., if they agreed with President Bush's foreign policy.
Defending his previous criticism that the Bush administration's foreign policy is "arrogant" and a "bunker-mentality," Huckabee attacked his Republican rival, suggesting he had better foreign policy bona fides.
"When I made those statements, there were times that we gave the world the impression we were going to do whatever we wanted to do," Huckabee defended.
Romney shot back: "I don't agree that the administration suffers from an arrogant bunker mentality," referring to a claim Huckabee made in a recent article in Foreign Affairs.
Romney a Target of Attacks
"Did you read the article?" Huckabee asked.
"I did read the article. I read the entire article," Romney responded.
Then Huckabee accused Romney of switching positions on Bush's troop surge strategy in Iraq, arguing he had come out in favor of increasing U.S. troops in Iraq long before Romney.
"I supported the president on the war before you did," said Huckabee. "I'm not a person who is out there taking cheap shots at the president."
Romney fired back, accusing Huckabee of distorting his position.
"I also supported the troop surge," Romney said, "Don't try to mischaracterize my position."
"Which one?" Huckabee shot back. "It's not a personal attack, Mitt, because you also supported a timed withdrawal."
Jumping into the fray, Sen. John McCain, R-Ariz., argued that he alone among Republican presidential contenders criticized Bush's initial policy in the war on Iraq.
"We are succeeding now in Iraq. As we blame the president for the failed strategy, we should give him credit," McCain said.
Former Sen. Fred Thompson of Tennessee agreed that the United States went to war in Iraq with too few troops.
Former New York Mayor Rudy Giuliani said Bush "got the big decision of his presidency right ... when he put us on the offense against Islamic terrorists."
The candidates sat beside one another in a forum Gibson said he hoped would be more of a conversation rather a debate.
McCain, Romney Trade Barbs
But the conversation turned explosive as the leading candidates in New Hampshire sought to draw distinctions.
Romney and McCain quickly began sparring on immigration, with McCain angrily denouncing the attack ads Romney has launched in the state that accused the Arizona senator of supporting "amnesty" for illegal immigrants.
"You can spend your whole fortune on these attack ads, but it doesn't make it true," McCain said.
"It is a form of amnesty," Romney argued. "That's your plan, and that plan is not appropriate. ... They should not be given a special right to stay here."
When McCain accused Romney of distorting his position, the former Massachusetts governor shot back: "Are they sent home? Are they sent home?"
"Some of them are, some of them are not, depending on their situation," McCain said.
The attacks turned personal when McCain delivered a sharp jab at Romney's latest strategy of attempting to position himself as the "change" candidate.
"I just want to say to Gov. Romney, we disagree on a lot of issues, but I agree you are the candidate of change," McCain said, a veiled swipe at Romney's new positions on on abortion and same-sex marriage.
Romney shot back: "The continued personal barbs are interesting but unnecessary."
Meanwhile, McCain tried to position himself as the candidate of experience, best able to face what he called "the transcendent challenge of the 21st Century, and that is radical Islamic extremists."
Turning toward McCain, Romney said that strategy wouldn't work if Sen. Barack Obama, D-Ill., was the Democratic nominee.
"If you think that making that argument as a Republican, that you have more experience, and have been around longer in the Senate, that you know the Senate cloakroom better than he does, that's not going to work," Romney said.
McCain Leading N.H. Poll
The debate came at a crucial time in New Hampshire, with McCain is looking strong in the state after his campaign all but collapsed this summer. Romney is working to win the support of Granite State voters after a disappointing finish in the Iowa caucus.
The latest WMUR/CNN poll released just hours before the debate began had McCain leading Romney in the Granite State by 6 percentage points, with the Arizona senator showing 33 percent support and the former governor 27 percent.
Former New York Mayor Rudy Giuliani garnered 14 percent. He has made frequent visits to the state and spent $2.5 million on television advertising there, according to data from the Campaign Media Analysis Group, an independent organization that tracks campaign spending.
Former Arkansas Gov. Huckabee, whose popularity among evangelical Christians helped him win the GOP caucus in Iowa, showed 11 percent support in New Hampshire, according to the WMUR poll.
The former Baptist minister had campaigned in New Hampshire, and his support for tax increases as Arkansas governor and his brand of economic populism isn't an easy sell with voters in the anti-tax, anti-big government state.
While Huckabee intends to campaign hard in New Hampshire until Tuesday, his next real test is the Jan. 19 South Carolina primary, where his prospects look better.
Poll: McCain Leads
"We're going to have to go convert a lot of people in New Hampshire in the next five days. A big tent revival out on the grounds of the Concord state capital," Huckabee told ABC News senior political correspondent Jake Tapper before the debate.
Other Republican candidates have hardly registered a blip on the radars of voters in the state. The latest poll has Rep. Ron Paul, R-Texas, at 9 percent support, and former Sen. Fred Thompson of Tennessee and Rep. Duncan Hunter, R-Calif., tied with 1 percent support each.
Romney, the former governor of a neighboring state, has poured resources into New Hampshire, spending millions of dollars in the Granite State on television ads and building a campaign infrastructure. He has not detailed to reporters how much of his own fortune was spent there.
McCain, who defeated George W. Bush in the New Hampshire primary in 2000, has an edge among the state's independent voters.
And in a state that has a history of making or breaking presidential runs, candidates are pushing through exhaustion after Iowa, trying to woo the state's crucial independent voters with a message of "change."
The race has turned ugly between Romney and McCain, with the former Massachusetts governor trying to paint the Arizona senator as a Washington insider.
"I am responsible for the biggest change that has saved American lives," McCain argued Saturday at a campaign event, referring to his years-long call for the troop surge strategy in Iraq.
"It's one thing to say it; it's another thing to do it," Romney said Saturday in Derry, N.H., arguing his record in business and government proves he can overhaul a dysfunctional Washington.
Romney has also begun hammering the Arizona senator with a steady stream of negative ads in the state.
One such ad says, "He [McCain] even voted to allow illegal immigrants to collect Social Security."
But Romney went into the debate Saturday win a small victory under his belt after winning the Wyoming Republican caucus, giving him most of the 12 delegates at stake there.
Candidates debated Saturday night knowing that New Hampshire may reset a Republican presidential contest that has yet to find its front-runner.
A loss in the Granite State would further erode the candidacy of Romney, who has spent about $7.3 million on ads in New Hampshire, more than twice the $3.5 million spent by McCain, according to the Campaign Media Analysis Group.
During the first nine months of 2007, Romney dumped $17 million of his own fortune into his campaign. His campaign said this week that he contributed even more money during the fourth quarter.
While Saturday's ABC News debate didn't provide any clear winners, Romney's leading New Hampshire rivals demonstrated their willingness to go for his jugular in the hopes of wounding the once-frontrunner before the Jan. 19 South Carolina primary.
Post-debate, Romney's campaign were busily spinning the attention their candidate received.
"If they are ignoring you, they aren't worried about you," said Romney's spokesman Kevin Madden.
"He showed the greatest degree of poise on the stage," Madden added.
At a post debate party, Romney said, "I am happy to go to debates where all they talk about is me."
ABC News' John Berman contributed to this report.