Trump wants to secede in small, categorical ways. California wanting secession is the Left speeding up the process that most of the Right has always wanted anyway. The American Left is starting to get over its equation: Leftism=Globalism. Secession will soon no longer be associated with racism, but with collections of affinities.
For people worried about the immigration issue, immigrants integrating into smaller, independent and sovereign communities would likely go a lot smoother.