This is always the case with just about anything. Whenever there is talk about the stock market reaching some high point and would never crash again, we know that is the absolutely right time to sell.
The same goes for the bottom. As the saying goes "it is always darkest before the dawn". This phrase was probably coined a millenium ago and still holds true.
So, from what I can tell. If people are saying that the Republican Party in CA is doomed. Maybe we've reached bottom and we can expect a turn-around. Hey, miracles do happen.
The generational differential, which benefited the GOP in the 1980s and 1990s as white baby boomers dominated the electorate, also will work against Republicans as whites retire, or die off, in large numbers while much-younger Latinos become the dominant worker bloc and their children fill the schools.
population will be U.S.-born citizens who will be legally entitled to vote as the role of immigration, legal and illegal, in population growth shrinks.
Finally, there is geography. While California's coastal counties have, for the most part, been strongly Democratic, Republican legislative and congressional candidates have fared relatively well in inland areas, such as Southern California's Inland Empire and the Central Valley.
However, the Latino population surge heavily affects what have been GOP-leaning inland areas. We saw hints of that in the redrawing of legislative and congressional districts after the 2010 census. We'll see more of it in the decades ahead.