Who can vote in primaries and caucuses

Depending on voter eligibility conditions,
primary elections may be open or closed (see Figure 1). In an open primary, a registered voter can vote in the Republican or Democrat primary, regardless of party
membership. However, voters cannot vote in more than one primary. In a closed primary, a Democrat-registered voter may only vote in a Democratic primary, and so on. Intermediate systems have also been
used, such as the semi-closed primary, in
which participation is open to both registered party members and unaffiliated voters.
Nevertheless, unaffiliated voters may choose which to vote in, while registered voters
may only vote in the respective party primary.