Lilliana Mason uses extensive social psychology research to explain how today’s polarization works. The two parties have become heavily “sorted”, and victory for the “team” eclipses attention to actual issues. She concludes:
The social sorting of American partisans has changed the electorate into a group of voters who are relatively unresponsive to changing information or real national problems. The voting booths are increasingly occupied by those who fiercely want their side to win and consider the other party to be disastrous.
And there are real effects: