Secession is not possible when EVERY large urban city in every RED state and surrounding counties are controlled by leftists. We can’t wall up every big city even as much as I’d like to.
It IS totally possible. A red state(s) could secede then form a new federal government plus armed forces and clamp down on the cities. Cities are small area - big population. Ugly yes but do-able.
The blue states own the cities but they can't clamp down on the country side. Ask the Viet Cong about that....
We should try to wall off our personal finances.