In congressional races, Kevin McCarthy and Janice Hahn won't be unopposed in the fall. McCarthy actually has four write-in opponents, a Democrat, a Republican, a Libertarian, and an NPP. Hahn will face a Peace and Freedom candidate.
In the assembly, Eric Linder is a Republican in a 53% Obama seat. Democrats had a candidate but that candidate failed to submit the proper paperwork in March. Two Democrats and a Libertarian qualified as write-ins. In 2012, Missouri Democratic senator Claire McCaskill meddled in the Republican primary to help her preferred opponent to win. As I've chronicled, Democrat Ro Khanna got a candidate on the ballot that may help him make Top Two. If Riverside County Republicans were like those Democrats, they'd give a push to the Libertarian candidate. Write-in candidates aren't on the ballot and remain unknown to almost every voter. If a Democrat were on the ballot, he'd receive enough votes to finish second. Since they're write-ins, a little promotion with one mailer could vault a candidate into top two.
Republicans didn't have a candidate in AD-21, a seat Carly Fiorina won in 2010 seat where the Democrat was unopposed. Jack Mobley, the losing 2012 candidate, is the sole write-in.