That’s fine. Immediately halt all U.S. spending in California. Remove all military personnel and close bases, fire all federal employees in CA and close all the federal courts in CA. Remove all elected CA House members and senators from the U.S. Congress. Not one penny spent on CA.
Allow one year for CA residents to move out and still maintain their U.S. citizenship. See how fast the U.S. recovers and thrives and how fast the Nation of California collapses.
You didn’t mention cutting off electricity generated in the US. Let them figure out how to generate their own. Oh, and drinking water for LA coming from the Colorado River? That’s out until they sign a treaty.
And send armed forces in to collect payment on what CA owes to fedgov.
Imagine all the federal college aid being cut off.
All the babies from chinese and mexicans NOT being us citizens.