Who's who in the Republican zoo
Washington - Going into Super Tuesday, four challengers remain in the hunt for the Republican party nomination to take on US President Barack Obama in the November 6 general election:
Mitt Romney is the clear frontrunner and will emerge from Super Tuesday as the presumptive nominee if he wins the crucial state of Ohio, adding to likely victories in Idaho, Massachusetts, Vermont and Virginia.
The former governor of liberal Massachusetts has struggled to connect with the conservative core of the Republican party, who worry about his past flip-flopping on issues such as abortion and gay marriage.
Romney, who racked up an estimated $200m fortune as CEO of Boston private equity firm Bain Capital in the 1970s and 1980s, has also risked alienating working-class voters with a string of wealth-related gaffes.
Whether he is offering one-time rival Rick Perry a $10 000 bet in a live debate or boasting that his wife drives two Cadillacs, his campaign has been plagued by remarks that make him seem out of touch with ordinary Americans.
Romney, aged 64, argues that he - unlike his rivals - has spent his life outside Washington's corrupt politics and that he alone has the business acumen to rescue an American economy being ruined by Obama's policies.
The man credited with saving the 2002 Salt Lake City Olympics from bankruptcy would be the first Mormon presidential nominee, going one better than his father, George Romney, who lost out to Richard Nixon in 1968.
The main challenger
Rick Santorum is favoured to win Oklahoma and Tennessee and could take North Dakota, but it is a victory in Ohio that he desperately seeks.
His path to the nomination relies on convincing Republican primary voters that he alone can beat Obama in Rust Belt swing states like Ohio and Pennsylvania.
The 53-year-old devout Catholic revived his faltering campaign with a surprise sweep of three states on February 8, shaking up the race with his faith-based brand of Republican populism.
His consistent message of "Family, Faith and Freedom" has found a ready audience across the American heartland, where evangelicals make up a key voting bloc.
In an intensely personal speech following his early win in Iowa, Santorum stood in sharp contrast to Romney as he described his roots in Pennsylvania's coal country, where his grandfather worked in the mines until he died at 72.
"I knelt next to his coffin. And all I could do - eye level - was look at his hands. They were enormous hands. And all I could think was those hands dug freedom for me," he said.
The Georgia primary, in terms of delegates the biggest prize on Super Tuesday, has come at just the right time for 68-year-old Newt Gingrich.
The thrice married former House speaker served as congressman of the "Peach State" for 20 years and holds a seemingly insurmountable opinion poll lead there.
That win should give him a chance to reset his campaign, and with Alabama and Mississippi looming the following week, it is not inconceivable that we might see a second Gingrich surge, based on taking the Deep South.
The Republican Party's self-proclaimed philosopher king, whose masterstroke "Contract for America" reform plan helped Republicans recapture the House in 1994 elections, has come back before.
Struggling after New Hampshire and targeted with the first question of a live debate in South Carolina, Gingrich was asked to comment on the bombshell allegation from an ex-wife that he had once requested an open marriage.
With his presidential hopes hanging in the balance, Gingrich struck out at the "destructive, vicious, negative nature of much of the news media", saying it was "as close to despicable as anything I can imagine".
The stunning counter-attack played brilliantly to the innate conservative distrust of the liberal media and transformed him from villain to hero.
The delegate hunter
The established wisdom is that unconventional Texas congressman Ron Paul is too old, too radical and too far removed from Republican orthodoxy to be a viable contender for the nomination.
Try telling that to the spry, 76-year-old Paul and his wildly enthusiastic supporters, most of whom are less than half his age.
The libertarian-leaning lawmaker has pledged to remove US troops from all overseas bases, lift sanctions on all countries - even Cuba and Iran - abolish the Federal Reserve, and end the war on drugs.
Paul is all about delegates. His campaign has conducted an intensive on-the-ground effort aimed at scooping up as many delegates as possible, choosing its battles carefully and competing only where he has a realistic chance.
If the race continues to be tight it is possible that no winner will emerge before the Republican convention at the end of August, in which case a victor may have to be decided by backroom brokering.
In such a scenario, Paul could play the role of kingmaker. His delegate haul will certainly give him a role in driving his small government beliefs into the Republicans' 2012 policy platform.