How South Dakota's Republican Primary Runoff Works

South Dakota uses a partially closed primary election system. Registered Republicans may vote only in the Republican primary, while registered Democrats vote only in the Democratic primary. Independent and unaffiliated voters may participate in the Democratic primary but generally may not vote in the Republican primary.

Beginning in 2026, South Dakota requires a primary runoff for nominations for Governor, U.S. Senate, and U.S. House when three or more candidates compete and no candidate receives at least 35% of the vote. In that case, the top two finishers advance to a runoff election held eight weeks later, where the candidate receiving the most votes wins the party's nomination. This is the first statewide election cycle in which South Dakota's runoff law has been triggered.