Washington's primary history

1935: Washington adopts a "blanket" primary that allows voters to pick a favorite for each office without regard to party label. Top vote-getter from each party advances to November general election.

2000: The U.S. Supreme Court invalidates a similar system adopted by California. Washington continues to use its blanket primary, though, when U.S. District Judge Frank Burgess sides with the state.

September 2003: The 9th U.S. Circuit Court of Appeals, relying on the U.S. Supreme Court's reasoning, overturns Burgess and sides with the state's political parties.

March 2004: After the high court declined to hear the state's appeal, lawmakers approved a top-two primary that allows the top two vote-getters to advance to the general election, without regard for party. But it also included a backup system, a Montana-style primary that requires voters to limit themselves to one party's voting.

April 2004: Then-Gov. Gary Locke vetoes the top-two part of the bill and leaves the state with the partisan Montana system.

September 2004: Washington holds its first Montana-style primary. It proves very unpopular.

November 2004: Voters approve Initiative 872, creating a top-two system, by a 60 percent yes vote.

May 2005: The political parties go to federal court, challenging the initiative as an unconstitutional infringement on their right to pick their own nominees.

July 2005: U.S. District Judge Thomas Zilly sides with the parties and throws out the top-two system, leaving the Montana plan in place.

August 2006: The 9th U.S. Circuit Court of Appeals upholds Zilly's ruling that the top-two system is unconstitutional.

Today: The U.S. Supreme Court agrees to hear the top-two case.