Build a time machine, travel back to 1993-94ish, and advise Pete Wilson to tone it down with immigration in his campaign.
While California's drift to a D state was inevitable, the CAGOP could have at least staved off the decline and made CA like a Massachusetts, Maryland, or Vermont type state in which GOP governors could still get elected while D's get elected to the White House and the Senate.
They will eventually get a Charlie Baker type through, particularly once the Dem legislature is seen as safely veto-proof. Newsom seems likely to really push the limits even in a liberal state, so whichever of 2022/26 is a Dem president midterm could be the opening.