Redistricting vs. Top Two
One of those impossible questions is answering which changes to the outcomes/behaviors in California elections should be attributed to which electoral reform. But there is an interesting case study that has developed in the Bay Area.
Much has been made of the defeats of Assemblymembers Betsy Butler and Michael Allen in 2012 as a demonstration of the power of the top two. I would argue those changes had much more to do with redistricting. Both members were drawn out of their seats and forced to run in very different districts, effectively nullifying the power of incumbency and subjecting them to attacks as carpetbaggers.
Less noted their ultimately victorious opponents were able to start raising money and building infrastructure long before they knew they would be challenging incumbents. Credible challengers tend to sit out challenges to incumbents precisely because the qualities that make them credible also tend to make them (more) rational and the risk-reward usually does not make sense. Would Marc Levine have started his race for Assembly if he knew he was going to be running against a sitting member, or did he stay in the race because he had already committed enough time and resources that it changed the equation of whether to stay in the race?
If I am right, then the power of incumbency will quickly take hold, top two or not. And with longer term limits we are heading towards a period of tremendous stability in the State Capitol (and in the California Congressional one the current wave of retirements work their way through the system). If I am wrong, top two will allow for increased challenges from all ends of the political spectrum and those new twelve year term limits won't look nearly as bright and shiny as many assume.
So how to find out? Well another of the major upsets attributed to Top Two provides the seed of the answer. Yes Eric Swalwell knocked off Pete Stark. But people forget that two arguably more credible opponents had bowed out of the race before his victory. Both of those candidates are not challenging sitting members of Congress: Ro Khanna is challenging Mike Honda in CA17 and Ellen Corbett is trying to turn the Top Two table on Swalwell.
If these two challengers are able to win then it will suggest the Top Two really is a threat to incumbents and credible challengers may increasingly decide they are not willing to wait their turn. If these two challengers go down a return to pre-primary normalcy is more likely (well until the next redistricting anyway).