Trump uses profanity for both cathartic and demagogic purposes, as a way to vent his frustrations and to stir up crowds. In 2016, he said it got him “standing ovations.” His supporters regard his cussing with the same esteem as the national anthem.
Swearing is supposed to denote authenticity, and Trump’s supporters love how authentically boorish he is. Liberty University President Jerry Falwell Jr. said that Trump “has single-handedly changed the definition of what behavior is ‘presidential’ from phony, failed & rehearsed to authentic, successful & down to earth.” At last, here is a president who is too real to be polite.
In a 2017 Pew survey, Trump supporters cited his personality, not his policies, as what they liked most about him. They like his personality more than his policies for the same reason that men like the nudity in X-rated movies more than the plots: The vulgarity is the point.