How South Dakota’s Primary Election System Works

South Dakota uses a partially closed primary system. Registered Republicans may only vote in Republican primaries, while the Democratic Party allows unaffiliated voters to participate in its primary elections. Voters registered with another political party generally cannot vote in a different party’s primary.

Unaffiliated voters may choose to vote in a participating party’s primary where permitted under party rules. South Dakota’s primaries are used to select each party’s nominees for offices such as U.S. Senate, U.S. House, governor, statewide offices, and state and local positions.

South Dakota has a unique 35% runoff threshold for gubernatorial and federal primaries. If a race for Governor, U.S. Senate, or U.S. House includes three or more candidates and no candidate receives at least 35% of the vote, the top two candidates advance to a runoff election to determine the party’s nominee.