What is the difference between a primary and a caucus?

A primary is administered by the state like a general election: polling places, secret ballots, and often early or mail voting, so participation takes minutes. A caucus is run by the political party rather than the state, and participants gather at a set time in schools, churches, and community centers to discuss candidates and indicate support, historically by physically grouping or by a show of hands, in a process that can run several hours. Because caucuses demand a specific evening and sustained presence, they systematically exclude shift workers, parents without childcare, people with disabilities, and anyone who cannot commit the block of time, and turnout is consistently a fraction of primary turnout.

Primaries are further divided by who may participate. Closed primaries permit only registered party members to vote in that party's contest. Open primaries allow any voter to choose which party's primary to participate in. Semi-closed variants let unaffiliated voters participate while excluding members of the other party. Some states use top-two or nonpartisan blanket primaries where all candidates appear on one ballot and the top two advance regardless of party, which changes campaign strategy considerably.

The trend has run strongly toward primaries. The number of states using caucuses has declined sharply in recent cycles, driven by turnout concerns, the operational problems that surfaced in several high-profile caucuses, and party rule changes encouraging primaries. Two structural points worth knowing. The parties, not the government, ultimately control their nomination processes, which is why rules on delegate allocation, superdelegates, and calendar order differ between parties and change between cycles. And the sequence of contests carries disproportionate influence because early results shape media coverage, fundraising, and the perception of viability, which is why the calendar order is itself a recurring subject of intense party dispute.