It will part company along red states/blue states.
I have been trying to picture for years what the map of the new countries would look like.
The problem for the liberals is... their coalition is divided by the whole middle of the continent. If the country broke up, the North East would be cut off from the west, which would I assume lead to at least 3 different countries (a western liberal one, a north eastern liberal one, and everything in the middle and south joining Texas to become the new conservative nation. No idea what would happen with Hawaii and Alaska.
Followed by a transfer of counties in ‘border’ blue states to the nearest red states, leaving the big cities as enclaves of poor Democrats.