In the case of Democratic Party of United States et al. v. Wisconsin ex rel. La Follette et al., 1980, the U.S Supreme Court ruled in favor of the Democratic National Committee (DNC). The DNC had challenged a Wisconsin law that allowed voters to participate in its primary without being members of or affiliated with the party, arguing it violated their First Amendment right to freedom of association by diluting their political message and forcing them into an unwanted association with non-party members. The court agreed, stating that while states have broad powers to regulate elections, they must respect constitutional rights when doing so - including political parties' rights to define their own membership criteria and structure internal affairs as they see fit.

In the dissenting opinion for Democratic Party of United States et al. v. Wisconsin ex rel. La Follette et al., Justice Brennan, joined by Justices Marshall and Blackmun, argued that the majority's decision to allow political parties to exclude non-members from participating in their primary elections was a violation of the First Amendment rights of freedom of association and speech. They contended that this ruling could potentially lead to discrimination against minority groups who may be excluded from party membership due to race or other factors, thereby undermining democratic principles. The dissenters also noted that allowing parties such broad discretion over their own rules might result in arbitrary or unfair practices which would not serve public interest.