Important John Myers for the LAT:

The new system has been especially tough on incumbents in the Legislature. In the five elections preceding the new system, only 8% of Assembly members and 2% of state senators faced a challenge from inside their political party. Since 2010, those numbers have skyrocketed.

In the state Senate, 28% of incumbents have faced same-party challenges. In the Assembly, the figure is 21%. In the congressional races, 12% have been same-party contests since 2010.

In one example, 40-year Democratic Rep. Pete Stark of Fremont was the first to be toppled by a younger challenger from within his party.

“The system has encouraged more candidates to run,” said Eric McGhee, a research fellow at the nonpartisan Public Policy Institute of California.

McGhee has spent several years attempting to measure the effect of not only the top-two primary, but also the state’s creation of an independent citizen commission to draw political boundaries.

Even when accounting for other factors, he said there is something to the argument that the top-two primary, by widening the net of potential candidates and voters, has led to at least incrementally more moderate lawmakers.