I think that there's a difference between a "Westerner" and a "Californian".
Agreed...
The past three Democratic Presidential nominees have all been (Or heavily associated with large states/Metro areas)....
Even Obama, who spent most of his younger years in Hawaii and Kansas, was somehow tied to Chicago, to the point where Trump appears to have developed an obsession with an entire city! HRC might have spent some time in Arkansas, and has some deep family roots in smaller town NE-PA, was somehow considered to be more associated with New York and DC, and to a lesser extent Chicago.
John Kerry, although he performed better than Dem nominees in '08/'12/'16 in rural and small town America, still got tied to the "Mass Liberal stereotype".
Al Gore, was the last Democratic nominee that could claim street cred for being from a smaller state, with relatively small population centers.
Bill Clinton, "The Boy from Hope" (Arkansas) definitely got major street cred in small-town and rural America.
The Democratic Party needs a breath of fresh air, meaning a different style of political leader, who comes from somewhere in the West (Outside of California), who can tell their personal life story and progressive political positions in a manner which is considered outside the realm of the Beltway and establishment politics, big city machines, and all that....
I think a Westerner could actually perform quite well in places like the Industrial Midwest, and generally in those parts of small-town America.... Shoot, just look at how some little known Senator from Vermont was able to mount a credible challenge to HRC, and is currently polling better than Trump at the national level.
I'm not going to delve into the prediction game of whom that candidate might be, but definitely I strongly suspect we'll see a few Westerner's throw their hat into the ring in 2020, that don't come from the great state of California....