----------According to the United States Constitution, a presidential election is to be held once every four years. The process of electing a president and vice president isn't an easy one; it begins long before Election Day. Candidates from both major and minor political parties and independent candidates begin to raise money and campaign at least one year in advance of the general presidential election. In order to officially represent a political party, a candidate must be nominated by that party.
---------The nominating process officially begins with the first state primaries and caucuses. These usually occur in February of the election year. Primary elections are held prior to the national conventions. The purposes to a primary are to determine who the delegates will be at the convention and to show voters" preferences for presidential candidates. In some states, caucuses are held instead of primaries to determine who the convention delegates will be. Caucuses are more local, but tend to take longer than primaries. It depends on the individual state's laws whether the convention delegates will be chosen by primary or caucus.
----------After the convention delegates are chosen, the actual convention takes place. The delegates cast votes for the person who will represent the political party in the general election in November. Thus, at the convention, the parties are not running against each other yet. The candidates are running against other candidates within their own party--republicans against republicans, democrats against democrats, and so on. In order to secure a party's nomination, a candidate must receive the majority of the vote from the delegates. Once the nomination election is completed, each candidate for president must then choose a vice-presidential candidate.
----------Once the candidates for president and vice-president are chosen, they campaign until it is time for the general election, which is held on the Tuesday following the first Monday in November.