According to the US constitution to stand any chance of becoming President of the United States of America, a candidate must be:
-at least 35 years of age
-a US citizen born in the USA
-resident of the USA for at least 14 years
The two major parties, Republicans and Democrats, choose their official candidate at national conventions organised in the summer. For the Republican party, this will be held from August 27-30, 2012.
At the convention, delegates from each of the 50 US states – plus delegates from Washington DC and a few US territories – vote for their preferred candidate. Their choice will have been decided by citizens in either a Primary or a Caucus.
A primary is a vote held by each state or territory to elect the preferred presidential candidate for that party. Some primaries are open - meaning any resident can vote regardless of political affiliation, while others are closed – for example in a Republican closed primary only registered Republicans are eligible to vote. The winning candidate will take that state’s delegates (and their votes) to the national convention.
A caucus vote is similar but much less formal vote, and is essentially a meeting of citizens registered with the relevant party. Card-carrying Democrats therefore may not vote in a Republican caucus. People attending the meetings – which are sometimes held in people’s living rooms - divide themselves into groups in different corners of the room according to their preferred candidate. Meanwhile undecided voters remain in the middle until they have been persuaded to join one of the candidate’s groups. Detailed rules for caucuses vary from state to state.
The number of delegates also depends on the size and population of each state. Large, populous states like Texas and California will send more than 150 delegates to the national convention, while smaller states such as Vermont may send fewer than 20. The number of delegates for each state changes between presidential elections, and is calculated according to how many Republicans or Democrats are elected to public office at that time.
Each state chooses whether to allocate delegates to candidates either by proportional representation or by ‘winner-take-all’. For example, in a ‘winner-take-all’ state, the candidate with the most votes will take all of that state’s delegates to the national convention. In a state using proportional representation, for example, and where there are 20 delegates up for grabs, imagine that candidate A wins 60% of votes and candidate B wins 40%. Candidate A will be awarded 12 delegates and candidate B eight delegates.
States also choose whether the delegates they will send to the convention will be ‘pledged’ or ‘unpledged’. ‘Pledged’ delegates are under obligation to vote for the candidate who won their state. ‘Unpledged’ candidates may in theory vote for any candidate they like, although in practice their vote is usually pre-determined by the result of their primary or caucus.