Unfortunately you cannot just wish away the cause-effect here. Did Democrats piss away a hundred million in South Carolina on a race Jamie Harrison was never going to win, or did Jamie Harrison get within striking distance because of that money and was the investment in party infrastructure and training of lower-level party coordinators going to pay off over the next decade? Texas did not turn blue, but the effort spent on Beto's race and now on MJ Hagar may build down-ticket strength and knowledgeable people who may end up turning the state in a few more cycles.

When I grew up California and Virginia were red states, and I am sure people then also said money spent there was not going to move the needle and was a waste. When you have a billion+ to spend on races sometimes a little hope now pays off in a decade or two even if you lose this race.

California hasn't had 2 Republican Senators at the same time since 1971. California became Democrat when the Republican Party realigned to the Southern Strategy, not because of campaigning.

Prior to 1992 the only time California had two Democratic senators was post-Watergate and then prior to that single term for Tunney you have to go all the way back to 1863 to get two Dem senators. California had frequently elected Republican governors (including one who went on to become president), had house delegations that were majority Republican for stretches of time, and except for Johnson's win in 1964 CA was a solid batch of electors for the Republican presidential candidate up until Clinton.

CA was a Republican state from the late 19th century up until the 1990s.