My first thoughts when reading the title were pretty much as Free Vulcan wrote.
The country is divided, and the two factions will never willingly unite again.
I said, "willingly".
The only "re-unification" will come by force.
After a struggle of some sort.
One side must defeat the other -- essentially, crush it out of existence.
Here's a "Fishrrman off-the-wall prediction" for ya:
This will happen after Mr. Trump is re-elected.
There will be actions taken by one state -- I'll guess by California -- that will be in open rebellion and defiance of the administration and the U.S. Constitution.
It will come to the point of "sending in the troops".
And that will happen.
Immediately, the other leftist states will "join" the rebellion -- Massachusetts, Vermont, Connecticut, New York, Maryland, perhaps Illinois.
They will side with the California Rebs against the United States.
And then....?