Let them go. The new ‘country’ will be divided into three or four nations within two years.
They’ll be non-contiguous.
If CA secedes, the remaining electoral math will be very stark to MA/CT/NY etc, and the only solution will be to band together.
WOuld be like having a US version of Gaza and the West Bank.
Sorry but California cannot secede and any attempts to do so will be crushed. It is basically only two city-states that wand to secede, the L.A. and San Francisco, and they can be isolated and starved out very easily. The American military could bring them to their knees in weeks as they go hungry and extremely thirsty.
Th n it will be pacification by force .