On May 21, the South Dakota Secretary of State determined that the initiative to establish a top-two system in South Dakota has enough valid signatures. Proponents of the initiative call it an “open primary” proposal. But past U.S. Supreme Court decisions, and all political science textbooks that talk about political parties, define “open primary” as a system in which each party its own primary ballot and its own nominees, but on primary day any voter can choose any party’s primary ballot. Proponents of top-two systems believe that “open primary” is an appealing label, so they have bent it to their own purposes.
In top-two systems, there are no party nominees nor party primary ballots. Instead every candidate runs in June and then only the two who get the most votes may run in November. South Dakota is already one of five states that bans all write-in votes.
No top-two ballot measure has passed since 2010, when the California measure passed with 53.7% of the vote. Since then the idea has been defeated by the voters in Oregon twice, Arizona, South Dakota, and Florida. Proponents of top-two vastly outspent opponents in all those instances.