Before the general election, the parties have to pick their candidates. For most of history, party bosses chose in back rooms. The primary took that power and handed it to ordinary voters.
A primary is an election in which voters, rather than party leaders, choose a party's candidate for the general election. It is the first round, where each party narrows its field down to a single nominee.
It was a Progressive Era reform aimed squarely at the bosses. Before primaries, party nominees were typically chosen by insiders in conventions and smoke-filled rooms. Reformers introduced the direct primary to take that power from the machines and give it to the voters.
Primaries come in types that matter. In a closed primary, only registered party members can vote in their party's contest. In an open primary, any voter can participate in either party's primary. The rules shape who has a say in choosing the nominees.
They have grown enormously powerful, especially for president. The modern system of state-by-state presidential primaries, where voters award delegates to candidates, replaced an older era when party leaders dominated the choice. Now the nomination is won in public, primary by primary.
