D has a semi-closed primary system, in which a political party may invite only its own party members and voters registered as Independents to vote in the party's primary. P notified the secretary of the Election Board that it wanted to open its upcoming primary to all registered Oklahoma voters, without regard to their party affiliation. Pursuant to § 1-104, the secretary agreed as to Independent voters, but not as to voters registered with other political parties. The LPO and several Republican and Democratic voters (Ps) then sued for declaratory and injunctive relief in the United States District Court. The District Court found that D's semiclosed primary system did not severely burden Ps' associational rights. Further, it found that any burden imposed by the system was justified by D's asserted interest in 'preserving the political parties as viable and identifiable interest groups, and ensuring that the results of a primary election . . . accurately reflect the voting of the party members.' The Court of Appeals for the Tenth Circuit reversed: D's semiclosed primary imposed a severe burden on Ps' associational rights, and thus was constitutional only if the statute was narrowly tailored to serve a compelling state interest. Finding none of D's interests compelling, the Court of Appeals enjoined Oklahoma from using its semiclosed primary law. The Supreme Court granted certiorari.