The state-by-state primaries and caucuses are a competition to see which candidate of either party can amass the most delegates and win that party's nomination to run for president in the general election.

The Republicans require that the nominee win a simple majority of 1,191 out of 2,380 delegates. That magic number is 2,118 out of 4,142 for Democrats.

In the Democratic nominating race, the delegate count is based on the total of pledged delegates and superdelegates won by each candidate. Democrats are awarded pledged delegates according to the percentage of the vote they earn in each state. Superdelegates include Democratic National Committee members, U.S. senators, governors and other party leaders who do not have to declare loyalty to a particular candidate, but some do.

In the Republican nominating race, most states choose a "winner-take-all" method of awarding delegates, in which the candidate getting the most votes from a state's caucus or primary wins all of that state's delegates. Republicans also allocate a certain number of unpledged delegates -- state party chairs, party committee members and others -- to each state. These unpledged delegates are free to vote for any candidate at the party convention, but they are usually aligned with a specific candidate.