^ In Presidential year Republican candidates would mostly play defence in any case in California. Trump's candidacy only exaggerate situation. Luckily for them - Republicans lost almost all swingy districts in California before (like 36th, 52th and some other), so - they will not lose too much this year. In House i can imagine them having tough elections only in 10th, 21th and 25th, and, most likely, they will not lose more then 1 of them (Democratic candidates in these districts are far from being very strong)...
I think Emilio Huerta in CA-21 has the potential to be a very strong challenger, and either of the two Democrats in CA-25 could be contenders if given enough money. Michael Eggman in CA-10 is the one candidate I have serious doubts with, and I wish Jose Hernandez would give it another shot.
Should a localized wave hit California, I also think Ed Royce in CA-39 could be in trouble.
Frankly speaking - i have doubts. But - we shall see
My reasons:
-Romney only won CA-39 50-47, only a point better than his 49-47 margin in CA-25 which is agreed to be competitive.
-The district has a large and growing Hispanic population, as well as a large (29%) Asian population. If Asians and Hispanics are shifting heavily to the Democrats this election, and Hispanic turnout surges due to Trump, this could be competitive really fast. Especially if, as many on this forum predict, Trump loses Orange County.
-In 2012, Democrats unexpectedly won an Assembly seat in the area with similar demographics and party affiliation with an underfunded challenger against an incumbent Republican.
-Royce's challenger in 2012, Jay Chen, severely lacked in fundraising and had campaign ethics issues
-Democrats have a potentially decent opponent in former Brea Mayor Brett Murdock.