In US politics, the first round of an election campaign; the presidential election has an entire season of primaries. In most cases, the vote is restricted to members of one party - Democratic Party candidates run in their own primary, Republicans do the same. In some locales, independent voters are free to vote; in others, there are all-in-one "open primaries", in which party affiliations are officially ignored. If no candidate reaches a certain threshold of votes, there is a runoff.