Don’t secede as states, at least not yet. But, accomplish the same thing in the mid term by kicking out every blue “urban area” that is for big, expensive, totalitarian (eventually) Fed government.
Think on this model: Vatican City is a sovereign state w/in the city of Rome, a capital city w/in the nation of Italy. Everybody gets along fine in the long term so long as they each mind their own business. They interact w/ each other thru international treaties; not oversight from a centralized (potentially totalitarian) body.
A similar relationship exists between Washington, D.C. and the rest of the USA. That District is outside any state – even tho it was cobbled together from bits of states. They have their own local government. They do not have any Senate representation and only a non-voting position in the House. For any national involvement they depend entirely upon Congress.
Apply those models to each red state.
To start, surely there is more than one predominantly red state that contains w/in it a modest, blue urban area. The test case. Convene a state assembly whose goal is to expel that area from the rest of the state. I sincerely doubt that there is any Fed constitutional provision that constrains what a state can do w/in its own borders so long as what they do doesn’t violate any existing Fed law. After all, when the state joined up many of those urban areas probably didn’t even exist. As to what happens to the expelled area, don’t care what happens to it, not my problem. Eventually, it will probably become another District w/in the US Fed – like Washington, D.C. Still US citizens. Still paying Fed taxes. But, nothing but neighbors to the enclosing reformed state. Oh, and they are not being disenfranchised. They don’t pay state taxes so they don’t need state representation.
The state convention will not officially consider a secession from the US. In fact, it ought to formally forbid any such open discussion so no Fed marshals show up to arrest seditionists. Each successive state convention will refine the process – learning from each that preceded it. During this process, the relationship w/ all of the other 49 states will remain the same, as will the relationship w/ the Fed.
Keep in mind what is going on between all those new Districts and the “remaining” states (i.e., don’t forget, until a total breakup occurs we are all 50 states and some Districts). Urban centers produce little food. They will have to import it from the surrounding red areas. Ditto for energy. As to jobs, they can either let nearby “ferriners” commute in to do the non-industrial paper-pushing that is all urban centers do nowadays or they can do w/out that tax base, too. They can fuss and piss about all they want. But, unless they are willing to relive the Berlin airlift they will have to grow up right quick and get along w/ their new neighbors in a new way. How they do that can be a detailed sidebar discussion at each successive convention.