If the US balkanizes, "Democrat" and "Republican" isn't where the split will happen. Less than half the voting population even identifies with either party, ffs.

There's plenty of cultural, religious and legal splits that could lead to a split. California is the obvious example, which would have to split with or take over Nevada and Colorado for the river and the dam. Texans has never been shy about longing for their own microstate and the swamp south has about as much in common with Seattle or Illinois as they do with British Columbia, if that.