The ONLY “Republicans carry California in modern day presidential election” scenario I can imagine would be an “era of good feelings” type election where a sitting GOP president is defaced UNOPPOSED in his re-election bid. And even if that happened, a bunch of disgruntled RATS in CA would cast token protest votes for unpledged RAT electors and invalid write-in votes for RATS not on the ballot.
President Trump may well be running unopposed; see this odd behavior from hiden biden:
https://twitter.com/EddieZipperer/status/1322218253247303681