The temperature of the water is not rising evenly and they understand that they still have an escape that is viable. The frontier kept the pressure off the East Coast during the massive imigration waves of the 18th Century. The South and West provide such a relief valve for the gun grabboid states.
I really do not know where the point of change is. If one looks at the American Revolution in 1772 independence was not gennerally cosidered to be a viable option but by 1775 the war had started.
Stay well - Stay safe - Stay armed - Yorktown