The question of whether the United States could fragment has been with us since the beginning and reached its culmination, of course, during the Civil War.
It continues to linger, of course, as many immigrants appear to be here solely for economic opportunity and our elites cringe at the concept of assimilation. All in all though, surveys indicate that for all of the screaming, Americans hold some very strong bonds. Even our politicians haven't reached the severe personal divisions that can be found in Britain and, to a much greater extent, in France and Italy.
Part of our glue is pragmatism. Americans will listen to the ideologues if they propose something that works. The Street Smarts Test that is applied by the average voter saves us from the fanatics. I recall a person who observed that you can put together a sensible argument that the voters have always chosen the best candidate for president. Partisans will object, of course, and yet the less passionate are one of the keys to our preservation. It may dilute the passion but it also dilutes the poison.