With candidates for the 2020 Democratic nomination popping up like mushrooms after a rain, it is worth noting that in the last two presidential year primaries, between 58% and 62% of the California votes were cast early by mail. The Iowa caucuses are on February 3, 2020, and the California primary is on March 3 [Super Tuesday], but early voting in California starts the day of the Iowa caucuses. In other words, it is not the case that someone can spend all of his or her time and money on Iowa, New Hampshire, Nevada, and South Carolina, and therefore hope to do well in California, because by then most of the votes in California will have been cast.
Of course, the first voting and caucusing will be preceded by innumerable debates, during which some hopefuls will flourish and others will wilt.
Bernie is apparently trying to recruit some women and African-Americans for his campaign team to overcome his weakness there.
It remains to be seen whether Trump will make it all the way to 2020.