I really doubt that California will secede from the United States of America. Rather, they will seek the impeachment of trump after the first error.
I don't think that Trump can be impeached with ease. Right now, there is a Republican majority in both the Senate and the House. Impeachment is possible only if a large number of RINOs side with the Democrats. And any chance of that seems extremely remote.
To me Trump is a time bomb, so that can change overnight. At the moment, he is clearly overwhelmed with what happened. But let's just wait till he fully settles in.