In practice it would never happen, for many reasons, but strategically California leaving would leave liberals every else totally in the lurch. The balance in the rest of the US would swing decisively towards the right. Would California rather be part of a closely divided nation that allows it a great deal of self-government, or be totally self governing and neighboring a very right-wing nation?
You know, just now reading about #CalExit for the first time, I’m struck by their stupidity. Not in the way you’d think, but in what they think is going to happen to them as a result of Trump. California is part of a federal system where they can do mostly what they want. Republicans respect that a lot more than Democrats do. Is the issue that Californians are actually afraid Trump will oppress them, or that they can’t stop Alabama from oppressing minorities? If it’s the former, they are just wrong. If it’s the latter, secession makes the problem worse.
I don’t think the #CalExit crowd is thinking strategically about what it does to other liberals “behind enemy lines”, but then again, I don’t really think the #CalExit crowd is thinking at all (although, by all means, I hope this irrationality continues all the way up to the point where we can take a star off the flag, or promote Puerto Rico as an alternate heavily-Hispanic state).
The basic problem in Western countries is the growing cultural gap between elites and the working class. In the US the gap between the elites and racial minorities, while still enormous, has been falling because elites have made a conscious effort to bridge it in recent decades. By contrast the gap between elites and the white working class has been growing and has now reached alarming proportions.
Meanwhile the white working class has its own set of pathologies which fuel right-wing politics. However the onus for bridging the gap lies mainly on the elite who have the cultural power and intellectual resources to do it. Part of the solution is about policy but a lot of it is about symbols and culture.
I think Obama understands this as did Bill Clinton but much of the Democratic elite doesn’t and there is only so much even a President can do.
Republicans have to show more respect to minorities as well. To get back to the point of the OP, we need to disconnect party from identity. I realize we’ll never get to a utopian state where how much money you make, your religion, your race, your sex, or your marital status won’t influence your allegiance, but right now those aspects are just too determinitive of your likely party affiliation.
One way to reduce that pull is to not treat those who vote for the other party as the enemy or disrespect them.