Assortative mating serves to intensify this polarization. It amplifies an already significant ingroup-outgroup mentality around contentious social issues. Social and cultural issues create severe disagreement because they trigger the emotional part of the brain: the disagreement challenges a core part of group identity. This is exactly the type of schism that an arrogant demagogue like Trump exploits.
Trump was able to convince rural and working-class people that he was the answer to their collective malaise. Economic anxiety, which Never Trumpers are so wont to point out as the reason for his success, is intimately tied to cultural issues, because the anxiety is seen as a product of unfair cultural decline. You didn’t lose your job because your skill set didn’t match a changing economic reality. Instead, it was the result of a rigged system that benefits the elite, liberal urban centers on each coast and their progressively government-dependent constituents, at your expense.