But this is why California secessionists have such an advantage.
Maybe. But it gets harder and harder for the Communists in charge of California to make that argument when almost all they are concerned about is privileging foreigners in the US against Americans.
All Trump would have to do is declare California to be in a state of insurrection, arrest its politicians and place the state under a military governor. Then commence Operation Wetback II.
Would there be riots? Probably. But why should I care if LA or Oakland burns itself out? Cut-off news and telecommunications, and make it plain that state employees need to fall in line if they wish to get paid. Heck, just offer those who stay on the job an emergency bonus.