The U.S. Supreme Court case California Democratic Party v. Bill Jones, Secretary of State of California (1999) revolved around the constitutionality of a Californian law that allowed voters to vote in any party's primary election, regardless of their own party affiliation - also known as "blanket" primaries. The Democratic Party argued this violated their First Amendment right to freedom of association by allowing non-party members to influence candidate selection. The court ruled 7-2 in favor of the Democrats, stating that political parties have a constitutional right to prevent non-members from participating in their primary elections if they so choose. This decision effectively invalidated blanket primaries and affirmed the rights for political parties to determine who can participate in selecting its candidates.

In the dissenting opinion for California Democratic Party v. Bill Jones, Justice Scalia argued that political parties are not private associations but public entities because they play a crucial role in the electoral process. He contended that states have a legitimate interest in structuring their electoral system to ensure broad representation and prevent factionalism, which can be achieved through open primaries. In his view, allowing political parties to exclude non-members from voting in their primary elections could lead to polarization and extremism as candidates cater only to party members' views rather than those of the broader electorate. Furthermore, he disagreed with the majority's interpretation of previous case law on this issue and believed it was inconsistent with democratic principles.