It's not just the political divides that have become so deep, it's the cultural (and psycho-social) ones from which the politics emerge that have become irreconcilable. "Right" and "Left" cultures in the US now contain points over which compromise is difficult-to-impossible...true binaries that are diametrically opposed.

It's that psycho-social thing that's probably the deal-breaker for any sort of unity. I would venture to say that when considering their socio-political identity, the majority of Americans now identify more with their "Left" or "Right" status (often annoyingly described as "Rep or Dem") that they do as "American.' They try to deny that by claiming that their side are the "true Americans," but that fallacy does nothing to alter that hierarchy of self-identification. This behavior occurs all over the social/political spectrum, I should point out.

Moreover, in our digital age people are beginning to identify more with their interest communities than with their physical locations. The ramifications of this switch are huge (and it's by no means restricted to - or even taken to its greatest extreme in - the US).

I can't see this ending, at some point in the not-too-distant future, in dissolution of the union into regional polities. Can't come any too soon as far as I'm concerned, and my main hope is that it's as bloodless as possible.