As more than 20 states prepare to vote in US presidential primaries and caucuses, Denis Stauntonprofiles the Democratic and Republican front-runners, and the six states that could prove crucial in deciding the nominees
After a month of closely fought contests for one state at a time, the race for the White House goes coast to coast next week when more than 20 states vote in primaries and caucuses Super Tuesday.
As the field narrows in both parties, the race is now all about winning the delegates who will choose the parties' nominees at national conventions in late August and early September. After all the drama of January's contests, no candidate has won more than a few dozen delegates, but thousands are up for grabs next week.
For the past 40 years, national conventions have been little more than week-long displays of party unity, held long after each party's nominee has won a clear victory in the primaries. This time around, however, the race is so close in both parties - particularly among the Democrats - that candidates are counting every delegate to prepare for the possibility of a brokered convention.
Hillary Clinton and Barack Obama are vying for a total of 2,064 delegates in 22 states on Tuesday - a handful more than the 2,026 a candidate needs to secure the Democratic nomination. Four Republicans - John McCain, Mitt Romney, Mike Huckabee and Ron Paul - are competing for 1,081 delegates in 21 states, a few dozen less than the 1,191 needed for the nomination.
THE STATES IN play next week are not only geographically and demographically diverse, but they use varying methods of selection - some hold primaries while others stage caucuses, and some contests award all the state's delegates to the winner while others divide them proportionally.
Most states hold primaries, which are elections in which voters cast secret ballots at polling booths that are open all day. Some primaries only allow registered party members to vote but others are open to independents or even to members of the opposing party who change their registration on the day.
Caucuses are meetings of party members, who have to meet at a specific time and place to choose delegates to attend another meeting, which eventually determines the state's delegation. Participating in a caucus calls for a greater commitment than voting in a primary because it means standing up before your neighbours and publicly declaring your support for a candidate.
Most Republican primaries and caucuses are "winner takes all", so that whichever candidate receives the most votes - even if he fails to win a majority - carries all that state's delegates.
All the Democratic caucuses and primaries use a form of proportional representation that divides delegates roughly according to how each candidate fares, although the system is exceptionally complex.
Each state is assigned a number of delegates based on the number of votes cast in that state for the Democratic candidate in the last three presidential elections. A proportion of each state's delegates are awarded according to the performance of each candidate across the state, but most are chosen on the basis of the results within each congressional district. Each state also sends "unpledged" delegates - party leaders and elected officials who attend the convention without being committed to any candidate. Each congressional district typically awards between three and five delegates and a candidate must win at least 15 per cent of the vote to get a delegate. The system works in such a way that if Obama wins 55 per cent of the vote in a district with four delegates and Clinton gets 44 per cent, they will each be awarded two delegates.
To gain a real advantage in the congressional districts, a candidate must win more than 60 per cent of the vote or - better still - ensure that the other candidate receives less than 15 per cent. This is why Clinton is working hard to maximise her vote in strongholds like upstate New York, while Obama is hoping for a record turnout in his home state of Illinois.
At the Democratic national convention in Denver next August, the delegates chosen through caucuses and primaries will be joined by almost 800 "super-delegates" - members of Congress, state and national party officials and other notables who are not pledged to support any candidate.
Traditionally, the super-delegates swing behind the winning candidate but the Democratic establishment is deeply divided between Obama and Clinton and both candidates are energetically wooing these delegates, who will account for a fifth of the votes at the convention.
The first vote at the convention will be on a report from the credentials committee, which is usually a matter of no importance. This year, however, the committee must decide whether to seat the delegates from Michigan and Florida, who were stripped of their voting rights because they defied party leaders by scheduling their primaries in January.
None of the candidates campaigned in either state but Clinton won both and she is arguing that Florida and Michigan delegates should have their voices heard at the convention by voting for her. Most Democrats now expect the race between Clinton and Obama to carry on beyond Super Tuesday, at least until early March, when some more big states vote, and possibly right up to the convention itself. Next week's contests could prove decisive for the Republicans, however, as McCain seeks to capitalise on the momentum of recent victories by delivering a knock-out punch to Romney and seizing the nomination.