MANCHESTER, N.H. - The oldest man on the stage had the most fire in his belly on Saturday as the latest Republican presidential debate quickly morphed into a battle for second place as front-runner Mitt Romney, smiling almost beatifically at times, watched his rivals do pitched battle.

Ron Paul, the 76-year-old libertarian congressman who's in second place in the New Hampshire polls heading into Tuesday's state primary, came out swinging, taking on Rick Santorum and Newt Gingrich using the type of arguments rarely heard springing from the lips of a Republican.

He didn't regret calling Gingrich a "chicken hawk" earlier this week, he told the debate moderators.

Paul has assailed Gingrich for supporting the wars in Iraq and Afghanistan while failing to serve Vietnam; he accused the former speaker of the House of Representatives of getting several deferments to avoid serving in the conflict.

"I think people who don't serve when they could ... they have no right to send our kids off to war, and not to even be against the wars we have," he said.

When Gingrich objected, denying he had received a deferment but saying he was ineligible to serve because he was married with children, Paul scoffed.

"When I was drafted, I was married and had two kids, and I went," he said to decisively end the exchange.

Paul also praised civil rights activist Martin Luther King Jr. when asked about 20-year-old newsletters published under his name containing racist and homophobic themes.

"One of my heroes is Martin Luther King, because he practiced the libertarian policy of peaceful resistance," Paul said.

He then went on a positively leftist rant about how drug laws are enforced in the United States, pointing out that black men are incarcerated at disproportionate rates.

"How many times have you seen the white rich person get the electric chair?" he asked. "If we really want to be concerned with racism...we ought to look at the drug laws."

Romney, for the most part, was spared any damaging attacks from his rivals. They all made attempts to dismiss him as a mere businessman rather than an inspirational leader, and pointed to his work at an investment company that cost American workers jobs.

He brushed off the attacks, barely breaking a sweat as he did so.

Bain Capital created 100,000 jobs all told, Romney said, adding that a businessman had a better grasp on how to rejuvenate the economy than lifetime politicians.

"I'm very proud of the fact that the two enterprises I led were successful," he said, referring to Bain and another firm.

But it was Paul who created some of the debate's most crackling moments, including when he assailed Santorum. The former Pennsylvania senator came within a handful of votes of beating Romney in the recent Iowa caucuses and had increased support in the state in recent days.

"You're a big spender, that's all there is to it -- you're a Big Government conservative," Paul told Santorum as Romney stood between them, grinning.

"To say you're a conservative is a stretch, but you've convinced a lot of people of it."

The verbal showdown in New Hampshire showcased an altered political landscape in the Republican race: Santorum is now enjoying his moment in the sun, while Michele Bachmann -- who revelled in her own surge in August -- is out of the race.

In a Suffolk University poll released Saturday, Romney had the support of 39 per cent of the state's primary voters, with Paul in second place at 17 per cent.

But the survey suggested that Santorum had peaked in the state as he battled for third place with Gingrich and former Utah governor Jon Huntsman, all of them at about nine per cent.

The poll suggested Santorum's momentum slowed noticeably following an appearance before a college crowd on Thursday that saw him face tough questions -- as well as jeers and boos -- about his opposition to same-sex marriage and his support for the wars in Iraq and Afghanistan.

Santorum, however, kept up his attacks on Romney during Saturday's debate.

"Being a president is not a CEO. You've got to lead and inspire," he said.

With the primary looming, the Republican race has been punctuated by a series of nasty skirmishes among the candidates.

Gingrich, in particular, believing he has a score to settle, has spent the days since his distant fourth-place finish in the Iowa caucuses bitterly maligning Romney. The Wall Street Journal's Peggy Noonan referred to him as an "angry little attack muffin" on Saturday.

But Gingrich failed to score any knockout punches against Romney on Saturday, despite blaming his rival for a series of attack ads launched against him in Iowa. Gingrich's campaign is fighting back.

A 30-minute counter-attack to be released soon portrays the former governor of Massachusetts as a ruthless corporate henchman who trod upon blue-collar workers when he was head of Bain Capital.

The campaigns of Paul and Huntsman have also been in an unseemly duel. Huntsman accuses a Paul supporter of posting an offensive video that questioned his loyalty to the United States by featuring clips of him speaking Mandarin with his adopted Chinese daughter.

Paul supporters have pushed back, commissioning a web consulting firm that suggested the Huntsman campaign was behind the video in an attempt to spur a backlash against the Texas congressman.

Huntsman spokesman Tim Miller scoffed at the accusation.

"Their latest conspiracy theory is nothing more than an attempt to cover for one of their racist supporters," he said.

"The Paul campaign has botched the response to this shameful video from the beginning. Had they simply condemned the video and their supporter, we would be discussing the important issues facing our country."

Paul has been polling well in New Hampshire, where Huntsman has devoted more time than any other candidate attempting to woo its primary voters.

The Paul campaign is also taking aim at Santorum with a new ad airing in South Carolina, the scene of the next primary on Jan. 21.

"One serial hypocrite exposed," the ad says, showing clips of Gingrich. "Now another has emerged: Rick Santorum, a corporate lobbyist and Washington politician. A record of betrayal."