Clingman v. Beaver

Oklahoma's semi-closed primary system let only a party's own members and registered Independents vote in that party's primary. The Libertarian Party of Oklahoma (LPO) (plaintiff) wanted to also open its primary to voters registered with other parties, but the state election board refused; the LPO and some Democratic and Republican voters sued, claiming this restriction on cross-party voting violated their First Amendment associational rights. The district court upheld the law, and the court of appeals reversed.