[Lurking Libertarian]

the GOP still retains a bastion of support in the southern part of the state, anchored by conservatives in Orange County and the military’s heavy presence near San Diego.

Orange County went for Hillary in 2016, the first time the County went for a Democrat since 1936(!). Changing demographics is part of it, but Trump also lost a lot of college-educated white people who used to be solid Republicans. (Nationwide, he more than made up for that by picking up white working class voters who used to be Dems, but there aren't many coal miners in Orange County.)

[KC Burke]

I think their recent primary system was set up to make them a one party state.

Now there will be many congressional districts where a Republican isn’t even on the ballot in the General election.

[SoCal Pubbie]

The OC went for Hillary by about 5%, which translates to less than 40,000 votes. I think that’s reversible in 2020, though it won’t matter statewide. There are a lot of foreign born voters here, and their offspring, like everywhere in California. The GOP, and Trump, really need to change the anti-immigrant image the media gives them. Hard to do when the media drives the narrative.