In 2004, Washington changed its primary ballot system to advance the two people with the most votes into the general election, regardless of party affiliation, instead of having voters choose their top candidates on a primary ballot just for their chosen party. That can result — and often does — in two candidates from the same party competing in the November election.
Washington’s primary system was challenged in the courts and eventually received the blessing of the U.S. Supreme Court in 2008.
When Washington voters approved the top-two primary system, the Democratic, Republican and Libertarian parties all challenged the new law, saying the U.S. Constitution gives Americans the right to affiliate with a political party of their choice. The parties said the law violates their right to pick the candidates for office and that someone who calls themselves a Democrat, for example, but doesn’t fit their ideals, could earn a place in the general election and force the party to support that candidate. The Supreme Court justices disagreed and sided with the voters. They even ordered the parties to repay the state for court costs.
Writing for the 7-2 majority, Justice Clarence Thomas said that overturning Washington’s primary initiative would have been an “extraordinary and precipitous nullification of the will of the people.”
The top-two primary system is the reason why in Washington elections for partisan offices on the ballot say the candidate “prefers the Republican Party” instead of just “is” a Republican.