I would hope any state with a secession plan has funding for a standing army, air force, and navy.
Or would certainly not ask for our help when a foreign nation showed up on its shores. The small part of me would chuckle as seeing Russian troops in CA, if it were not so serious.
If you want to leave, you can fend for yourself. And in California’s case, where would it get its currency? What would back it? The US could impose tariffs on what would amount to a non-influential country at that point to make the cost of doing business with the other 49 states prohibitive for CA.
They’d also have to return all land-locked federal land in the State, have massive layoffs (I’d assume we’d close LA Air Force Base, Edwards, and a host of others, or at least they’d become simply Air Bases), and the feds could incentivize major employers like Boeing to close down their ops and relocate to the actual US.
Most secession plans from States are just hissy fits from whiny, naive children.