US Republican presidential candidates led by front-runner Mitt Romney used their first big televised debate on Monday to lash out at President Barack Obama – but not at one another.

The debate in Manchester, New Hampshire, did little to define differences among the seven candidates in the unwieldy Republican line-up as White House hopefuls reserved their venom for Obama on the economy and foreign policy.

The civil exchanges left Mr Romney, who has a slight but consistent lead in the polls, still looking like the man to beat for the nomination.

Standing behind the centre podium in CNN’s ultra-modern studio, the carefully-combed Romney looked suitably presidential as he led the charge against Mr Obama.

“Any one of the people on this stage would be a better president than President Obama,” he said.

“Why isn’t the president leading? He isn’t balancing our budget and he isn’t leading on jobs. He’s failed the American people... And that’s why he’s not going to be re-elected.”

Michele Bachmann, a Congresswoman and leading light of the staunchly conservative Tea Party movement, momentarily upstaged the other six when she used her opening comments to announce that she had just formally registered her candidacy.

Ms Bachmann, the only woman on the stage, elegant in a pearl necklace and pearl earrings, pulled her punches when opportunities came to attack Mr Romney, but she almost shouted during assaults on Mr Obama.

“President Obama has failed his leadership,” she charged.

Newt Gingrich, a veteran Republican who was speaker of the House of Representatives in the 1990s, piled in to attack “the Obama depression”.

The presidential election is not until November 2012. But candidates were using this event – the first of many over the coming months – to solidify their sometimes-poor name recognition across the country and position themselves for a gruelling campaign.

New Hampshire is one of the first states to hold a Republican primary election in February, and results there can be crucial to a candidate’s momentum heading into follow-up primaries across the country and eventually to the party nomination.

For Mr Romney, already well known as a former Massachusetts governor and failed 2008 presidential candidate, the night required avoiding slip-ups and showing he was above the fray.

He managed that when former Minnesota governor Tim Pawlenty refused to press earlier attacks he’d made in the media on Romney’s introduction while governor of a universal health care plan in Massachusetts.

The plan, a model for Mr Obama when the President introduced a similar scheme nationwide, is widely detested among Republicans. Romney took the issue head-on and said: “If I am elected President I will repeal Obamacare.”

On foreign policy there was little daylight between candidates, who accused Mr Obama of failing America’s long-standing dominance on the world stage and bungling the bombing of Libya.

They all said they favoured bringing back troops now fighting in Afghanistan, saying nation-building was not the right US role.

“This is the first time we’ve had a President who doesn’t have a foreign policy,” Mr Romney said.

Ron Paul, the prickly and defiantly unglamorous Libertarian Congressman from Texas, drew applause when he said he wouldn’t wait for generals to tell him it was OK to withdraw from Afghanistan.

“If I’m the Commander in Chief,” he thundered, “I’d bring them home as quickly as possible.”

Also in the debate were former Senator Rick Santorum and pizza entrepreneur Herman Cain.

Main candidates taking part in the debate

Michele Bachmann: 55. Congresswoman often seen as an alternative to Sarah Palin: both are polarising Tea Party favourites, wildly popular among core supporters and loathed by opponents. She formally registered her candidacy just before the debate.

Herman Cain: 65. The former CEO of Godfather’s Pizza has never run for president and his outsider status, together with public speaking talent, has helped him grab an unexpectedly large early following with his pro-business proposals. He is the only African American Republican candidate.

Newt Gingrich: 67. Big beast in the party with decades of high-level experience, including House Speaker in the 1990s. But he is hampered by a messy marital record and now a turbulent campaign, with the bulk of his staff walking out.

Ron Paul: 75. A veteran of past campaigns, the Texas Congressman is a libertarian whose radical rethinking of US policies attracts dedicated supporters of the Tea Party type, but gives him little chance on wider political battlegrounds.

Tim Pawlenty: 50. Former Minnesota governor. His claim to fame is that he whipped overblown budgets into shape in Minnesota and did this in a state with strong liberal tendencies. But he has little name recognition and is seen by critics as lacking gravitas.

Mitt Romney: 64. Former Massachusetts governor. Polls make him the man to beat so far and he has the polished campaign machine of someone who already tried and failed to get the nomination in 2008. But some see the Mormon businessman as wooden and unable to fire up the country. His biggest liability among fellow Republicans is that he passed a health care plan as governor.

Rick Santorum: 53. A former Pennsylvania senator turned media commentator with a record of strongly-conservative values on social issues.

Not taking part in debate but considered possible front-runners:

Jon Huntsman: 51. Until recently the US ambassador to China, he has foreign policy experience and a moderate stand that could appeal to independents. Says he could declare in a matter of days.

Sarah Palin: 47. Started as a beauty queen and went on to show her steely side in Alaska where she became governor. Shot to stardom – and controversy – as vice presidential candidate in John McCain’s failed 2008 bid. Hasn’t declared yet but polls make her second only to Romney and she recently toured the northeast in a bus.

Texas Governor Rick Perry (61), former New York Mayor Rudy Giuliani (67) and New Jersey Governor Chris Christie (48), who have not declared, are all heavyweights who could enter the race and turn the contest on its head.

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