Maybe treat them like N.Korea and not permit them to house any missiles on our bases. As soon as the Feds see any kind of evidence of this beginning to happen, do a pre-emptive strike?
The thought of them seceding is just so tantalizing. If they do, and fail, and want to re-join, it would be the perfect opportunity to divide it into several states, clean out the riff raff and insane, and bust up the 9th Circuit.
They already remind me of North Korea. This Calexit stuff is all talking and feet stomping for more federal money. If they really did this, it wouldn’t end well for them and it would take decades for them to recover.