What characterizes a closed primary in U.S. elections?

A closed primary is characterized by the requirement that only registered party members can participate in the voting process to choose their party’s candidates. This system is designed to maintain the integrity and ideological consistency of the political party by ensuring that only those who are officially affiliated with the party can influence its candidate selection. This can prevent members of other parties from potentially swaying the outcome in a way that might not align with the party's values or goals.

In contrast, other options describe different characteristics. For example, an open primary allows any registered voter to participate, regardless of party membership. The mention of voting occurring in private locations is common to many types of elections, not specifically reflective of closed primaries. Finally, the statement about the primary being held at the national level only does not pertain to the definition of a closed primary, as primaries can occur at various levels (local, state, and national). Understanding these distinctions helps frame the operation and implications of different primary systems in U.S. elections.