First, California has a batshit crazy electoral system. Not quite as nuts-o as Louisiana, because nobody is that crazy, but close. California has everyone face everyone else in a primary. The top two vote-getters face each other in the general election, even if they are of the same party. Yeah, fucked up, right? The Louisiana twist is that they call off the general election if someone gets over 50% in the primary because nobody out-crazies
Anyway, this is a weird rule. Feinstein is facing someone who is... kind of a chump. Kevin de Leon is trying to mount a lefty challenge to Feinstein, who is a relative moderate. On our DW-NOMINATE scale, developed by Poole and Rosenthal, she's at -.265 on the -1 to +1 scale. That puts her to the right of the Democratic median, but she isn't exactly the Democrats' version of Susan Collins. She's still to the left of Angus King and Joe Donnelly and Amy Klobuchar and Chris Coons and Jon Tester and Joe Manchin and Tim Kaine and Mark Warner and Heidi Heitkamp and Claire McCaskill and Gary Peters and Tom Carper and Michael Bennet.
So, yeah. By all means, you fuckin' lefties. Purge DiFi. She's your enemy.
California is an odd state, though. A Republican can't beat a Democrat statewide, without odd circumstances (like the recall of Gray Davis, which elected the Governator), and... incumbents win. Here's where we factor in the electoral rule, though. One of two things happens. Either DiFi winds up running against some sacrificial lamb Republican and beats him to a bloody pulp because it's California in a midterm election with Trump as President, or de Leon makes it to the "general" election.
Now, what's the "theory," such as it is, behind the top-two model that California now uses? The idea is to reduce polarization. If primary voters just vote for the most wacko candidate, then you wind up with general elections consisting of a moonbat versus a wingnut, and either way, the winner is a wacko. If, on the other hand, you can have a run-off within a party, there might be some centrist pressure.
What if that worked? Hint: it doesn't, generally speaking, but what if it did?
In the primary, you've got Republicans voting for a Republican, and Democrats dividing their votes between DiFi and de Leon. Either DiFi winds up in a general against a Republican and crushes him, or de Leon gets more votes than the highest vote-getting Republican. Those Republicans, in the general election, then have a choice between the comparatively centrist DiFi, and de Leon. Whom do they pick? Probably DiFi.
Feinstein wins. Either way.
The safest bet is still Feinstein. If she doesn't crush de Leon in the "primary," the Republicans who face a "general" election between Feinstein and de Leon will pick her over the lefty.
We've seen this before. When Joe Lieberman lost his primary to Ned Lamont in 2006, he decided to run as an "independent," and the Republicans voted for him because the choice was him or Lamont.
It is hard for me to see how Feinstein loses.