So, we have lots of potential kinds of answers to that questions. Religious, philosophical, social scientific, economic, historical, political science, literary and ideological and most will deny Trumps behavior or election by the voters is a problem at all.
If his behavior does not cause harm, that would be great but pathological lying and delusional behavior usually causes personal problems if not wider trouble when the bad actor is in power.
Since the problem with Trump is his behavior, and that of the voters who gave him power, I say medically based brain science has the best chance of real answers. Behavior is a medical physiology and neurology problem.