What characterizes a closed primary?

A closed primary is characterized by the requirement that voters can only participate in the nomination of candidates for the political party with which they are enrolled. This means that if you are registered as a Democrat, you can only vote in the Democratic primary, and if you are registered as a Republican, only in the Republican primary. This system aims to ensure that party members have control over their candidates and prevents members of other parties from influencing the selection of a party's nominee.

In contrast, other types of primaries, such as open primaries, allow any registered voter to participate regardless of their party affiliation; in mixed or nonpartisan primaries, candidates from different parties are included on the same ballot for voters to choose from. Thus, the essence of a closed primary is its restrictive nature concerning who can vote in which party's primary, ensuring that only party members influence their party’s candidate selection.