The race to find a Republican challenger is already well under way. Throughout months of debate in the latter half of 2011, a succession of contenders rose to the fore before fading away.
Here is a list of the main candidates for a nod towards a conservative run at the White House
The former governor for Massachusetts is the perceived front-runner in the Republican race. The 64-year-old has in effect been running for the last five years, having failed to get the ticket last time around.
His main strengths are a good organisational structure and money, lots of it. Estimated to be in command of a personal wealth exceeding 200 million dollars, his team has access to the largest campaign fund - crucial in the primary stage.
On the downside, he is mistrusted by the Republican Party’s evangelical wing, due in part to his Mormon faith. In addition past positions on gay rights, abortion and healthcare have critics accusing him of flip-flopping on the issues and kowtowing to the right.
The former house speaker’s campaign got off to a disastrous start after the entire echelon of his top staff quit en masse. But strong performances during a series of televised debates saw the 68-year-old regain momentum, rising to the top of the polls before running out of steam and falling back down again.
Mr Gingrich is the most experienced candidate in the running, having held the third most powerful position in American politics - speaker of the House of Representatives. He is seen as an ideas man, with the intellectual prowess and debating skills to take on Mr Obama.
But he has baggage. As speaker he forced a deeply unpopular government shutdown and was disciplined by the house’s ethics committee.
Moreover his past infidelities do not sit well with the religious right. He cheated on his second wife with a staffer 23 years his junior, while trying to impeach Bill Clinton over his encounter with Monica Lewinsky. He also had an affair during his first marriage and divorced his wife while she was recovering from cancer surgery.
Until recently the governor from Texas was seen as a contender for the Republican crown.
Having entered the race late, his plain-speaking appeals to the party’s evangelical wing gained traction for the 61-year-old.
But then came the debating season and his weaknesses were exposed. In an excruciating 53 seconds in front of the cameras, Mr Perry attempted to outline the three government departments he would axe as president. He named two, and then got stuck. “The third one, I can’t. Sorry. Oops,” he explained.
His campaign has not recovered since.
Touted as more Sarah Palin than Sarah Palin, the Minnesota politician is a firm favourite of the Tea Party - the Republican Party’s socially conservative activist base.
Her campaign got off to a flying start, propelling her to the coveted position of the leading “anyone but Romney” candidate.
But cracks began to appear as the media and fellow candidates began to probe her on policy and experience. Ms Bachmann, a mother of five and foster parent of 23, has pinned all her hopes on a strong showing in Iowa - the first caucus in the race. Failure at that hurdle is likely to kill off any hopes she has of getting the Republican ticket.
Intelligent, experienced and possessing the ability to pull votes from the centre - Mr Huntsman could pose the biggest problem to Obama if he is chosen, but it is increasingly unlikely that he will be.
The mild-mannered 51-year-old has failed to get any momentum in the early running, with his polling amongst Republican voters languishing in single figures.
Aside from his low profile, Mr Huntsman’s main problem is that, as ambassador to China, he served in the Obama administration. In an increasingly partisan US political environment, such a move is seen as a betrayal amongst hard-line conservatives.
The 76-year-old Congressman has consistently polled well in the race to date, especially in conservative states.
He is seen as an arch-libertarian, calling for smaller government, the elimination of income tax and a dramatic roll-back in the US’s involvement overseas.
The former physician is looking towards a strong showing in the Iowa caucuses as a springboard to greater things. But his positions on some issues are seen by many to be too extreme to stand any real chance of winning the presidency, or the Republican ticket.
Having failed to make much impact during a series of debates with rivals, Mr Santorum has seen a surge of support since they ended. Latest polls suggest he could be in line for a morale-boosting top three finish in the Iowa caucuses.
An ardent Christian, his policies are shaped by his religious beliefs. But he is in danger of being squeezed in the race to get a nod from the Tea Party by other more candidates from the right, including Ms Bachmann and Messrs Perry and Gingrich.
The views of the experts
The old adage “Democrats fall in love and Republicans fall in line” is expected to kick in, delivering Mr Romney up as the challenger to Mr Obama come election time.
Adam Geller, Republican pollster and chief executive of National Research, believes the former governor of Massachusetts has the money and organisation in place to win the Republican nod.
“Mitt Romney is best placed for a long primary campaign. The polls will go up and down but this is a marathon not a sprint,” Mr Geller said.
He continued: “The candidate with the largest bank account and good organisation in every state is the best placed to win.
“And Romney has the advantage of having run for six years. And he already has a very impressive bank account.
“The other advantage is that Gingrich, Bachmann, Perry and Paul are splitting the anti-Romney vote.”
Bill Galston, former Clinton aide and political analyst at Brookings Institution, also believes that the party will eventually line up behind Mr Romney.
He said: “I think the Republican Party is engaged in a struggle between its head and its heart at the moment. The head clearly knows it should nominate Mitt Romney, but the heart wants something else entirely.
“We have seen cycles of ‘anyone but Romneys’, but in each case the latest contestant to dance out on to the stage has been found wanting.”
He added: “The conventional wisdom is there are three tickets coming out of Iowa. If the three tickets are Romney, Gingrich and Paul then it is a two-horse race, as no one thinks Paul is going to be the candidate.”