Such systems are not entirely new; California actually adopted a similar electoral method — a so-called blanket primary that allowed voting across party lines — in 1996. In 2000, it was invalidated by the United States Supreme Court after a challenge from several political parties. But the “top two” system in Washington State was affirmed by the same court in 2008.
This is very misleading. The top-two primary can produce contrasting results to a blanket primary.
With a blanket primary, all voters can vote in a primary regardless of party registration. A voter gets to select one candidate for each position. The voters can vote for a candidate of any party, and even choose candidates of different parties for different offices. The important thing is the result: The candidate running for the Democrat, Republican, Green Party, Libertarian, etc., nomination with the most votes gets that nomination. Democrats are still only competing against fellow Democrats and Republicans against fellow Republicans. This means you will still always have only one candidate officially representing each party in the general election. Independent candidates can still run in the general election.
With a top-two primary, this is not the case. A voter can select any candidate for any office, but only the two candidates with the most votes, regardless of party, go on to the general election ballot. This means you can easily have general elections between just two Democrats or just two Republicans. It is even possible that a crowded field of Republican candidates might cancel one another out, resulting in two Democrats on the general election ballot, even in Republican-leaning districts.
The example of Florida
In the Florida Senate race, with a blanket primary, Marco Rubio would likely win the most votes among the GOP candidates on the ballot. Kendrick Meek would likely get the most votes among the Democrats. Since Charlie Crist is running as an independent without a party affiliation, he would not even take part in the primary. The result would be a general election among Rubio, Crist and Meek. I’d put Rubio as the favorite to win with roughly 40 percent of the general vote.
Now, assume the state uses the top-two primary system. The results would be very different. All three candidates would be on the primary ballot. Only the top two, though, could go on to the general election. Given current polling, it’s likely the general would be a head-to-head match-up between Rubio and Crist. In this scenario, Crist is the favorite.
The design of election laws can have a huge impact on who gets elected. While the two systems might appear superficially similar, what they do is significantly different. A blanket primary still ensures the general election contains only one nominee from each party. The top-two system makes it possible that the general election would be a battle between two members of the same party.