On the other hand, parties aren't completely public entities; the Supreme Court has held that they are, in some senses, private associations, and their members thus have privileges over non-members. In the case California Democratic Party v. Jones (1999), the majority ruled that California's blanket primary, which allowed voters of any party or no party at all to choose among all candidates of all parties, was unconstitutional, in large part because it allowed people who were not members of a party to pick the party's nominees. Justice Scalia, writing the majority opinion, wrote:
[U]nder California’s blanket primary system, the prospect of having a party’s nominee determined by adherents of an opposing party is far from remote – indeed, it is a clear and present danger.... [A] single election in which the party nominee is selected by nonparty members could be enough to destroy the party.Those are strong words, firmly claiming that the party belongs to its members. Unaffiliated voters, by this logic, do not have a "right" to participate in a primary election; it is up to the party whether or not they want to include them. The decision of whom to nominate for office, the most important decision a party makes, should be left to those who have some stake in it, those who have claimed membership.*
So how does this square with Proposition 14, California's top-two primary? Doesn't such a primary (which takes place tomorrow) allow nonparty members to pick party nominees? Proposition 14 got around this by changing the definition of the primary election, following the guidance of the Court in Jones. The language of the proposition amended the state constitution to change primaries from party contests to "voter-nomination primary elections." So the primary in California no longer belongs to parties, but rather to the voters.
This is particularly interesting because in American politics over the past century, we have generally not drawn a distinction between the winner of a primary and the party nominee. That was part of the logic of creating primary elections in the first place: to create a clear, public, unambiguous determination of just who the nominee was. Now in California, as in Nebraska and Louisiana, the primary and the nomination have been decoupled, and the parties must resort to other means to converge support on a preferred candidate.
*I should mention that, back in 1942, E. E. Schattschneider argued that the whole idea that party "members" had some stake in its selection of candidates was absurd. Schattschneider noted that party members are not required to pay dues, perform duties, attend rallies, solicit votes, or even vote for their party's nominees. They don't need to notify anyone in their party if they wish to leave it:
Membership in a political party is therefore highly unreal because the party has no control over its own membership and the member has no obligations to the party.... In what sense is a partisan injured if he is deprived of the right to control an organization toward which he has no duties? The whole theory is chaotic (pp. 56-59).Obviously, this isn't the dominant view today among political observers. But it is a useful perspective when one considers the desired level of openness in a primary election.