California is 27% foreign born, only 37% white, and has nearly half its population speaking a language besides English at home. A republican staying within 10 points there would require a GOP landslide nationally.
W Bush lost CA by 9.96% in 2004. Has CA demographics changed that drastically since then?
No, but the Republican Party has. It's went from conservative hero Reagan giving amnesty to millions of illegal immigrants to candidate Trump calling for deporting every single person who is here illegaly. The GOP of Reagan and Bush is dead, and thus, so are its chances of ever competing in California.