A profile of the Republican front-runners
Mike Huckabee
The former Arkansas governor and Baptist minister has failed to replicate his early victory in Iowa and he now has little hope of winning the Republican nomination. Huckabee could play an important role as a spoiler on Tuesday, siphoning off conservative votes from Romney in narrowly fought states, which could then go to McCain.
Huckabee is concentrating on Alabama, Georgia and his home state of Arkansas, but he could also be competitive in Missouri, where his mixture of social conservatism and economic populism plays well among less well-off evangelical Christians.
Huckabee, who has run out of money, could withdraw from the race after
Super Tuesday but he is already being touted as a possible running mate for McCain.
John McCain
The Arizona senator, whose campaign was written off as dead only six months ago, now believes that he could secure the Republican nomination next Tuesday. Victories in New Hampshire, South Carolina and Florida have made him the clear front-runner, boosted by endorsements from former New York mayor Rudy Giuliani, who left the race this week, and California governor Arnold Schwarzenegger.
McCain should win his home state of Arizona, as well as New York, New Jersey, Delaware and Connecticut, all of which are "winner takes all" states. He has a good chance of winning at least half a dozen other states, and he expects to take most delegates in California, which uses proportional representation, and he could even win in Romney's home state of Massachusetts.
Ron Paul
The libertarian congressman from Texas, who wants to abolish income tax, restore the gold standard and bring all US troops home from overseas operations, has raised huge amounts of money and built up a passionate and extensive network of supporters.
He has failed to make the top three in any contest so far, however, and he is unlikely to make a significant impact on Tuesday.
Paul has the cash to stay in the race all the way to the convention and he will probably remain a candidate for as long as possible, if only so that he can voice his conservative dissent during Republican debates.
Paul, who ran as a Libertarian Party candidate in the 1988 presidential race, has not ruled out running as an independent this year.
Mitt Romney
The former Massachusetts governor has spent at least $40 million (€27 million) from his personal fortune on seeking the presidency and he is blanketing the airwaves with TV ads before Super Tuesday. Romney's best hope lies in a conservative revolt against McCain, who is viewed with deep suspicion by many within the Republican base.
While McCain looks for delegates on the east and west coasts, Romney is targeting the south, west and midwest, hoping to win states such as Colorado, West Virginia and Utah, and to pick up some delegates in California.
The former venture capitalist believes the race could go his way if he can keep the focus on the economy, something he has failed to do in recent days as McCain has questioned his support for the US mission in Iraq.