Final answer:
Members of the Republican and Democratic Parties choose their party's presidential nominee through a primary or caucus.
Step-by-step explanation:
Prior to their national conventions, members of the Republican and Democratic Parties meet in designated places within their state to choose their party's presidential nominee using the nominating method of a primary or caucus. In a primary, party members use a ballot to indicate their preferred candidate, while in a caucus, party members gather in predetermined locations at predetermined times to discuss and vote for their preferred candidate.