The Court's 7-2 ruling is a blow to the state’s Republican and Democratic parties, who argued that they have the prerogative to limit participation in primaries to registered members of the party.
Washington had a long history, dating back to 1935, of holding open primaries where the top two vote-getters from each party head to the general election. But in 2000, the Supreme Court ruled that such partisan blanket primaries were unconstitutional.
Then in 2004, Washington state voters supported a referendum to establish a nonpartisan blanket primary — allowing the possibility for the general election to feature two candidates from the same party — but the state’s political parties immediately challenged the decision in court, arguing that it violated their rights of association.
Writing for the majority, Justice Clarence Thomas said that overturning the state’s plan would have been an "extraordinary and precipitous nullification of the will of the people."
Justices Antonin Scalia and Anthony Kennedy dissented.
The Supreme Court decision affects this year’s primary, scheduled for August 19.
Reid Wilson of RealClearPolitics has additional perspective on the ramification of the Supreme Court’s decision.