re: What would the process of splitting the country up look like

It would take a Texas or a Florida to get things started. Smaller states could join in and make some sort of “Compact of Red States” that would begin to work together even as part of the current nation.

We’d eventually get to a point where we had two de facto countries, there would be 50 more years of this Cold War thing and eventually both sides would have leaders at the same time that would work things out.