Asking foreign countries to investigate and deliver dirt on his political opponents, which prompted an impeachment inquiry in the U.S. House of Representatives, is the most recent example in a long string of norm-shattering behaviors. Other examples of flouting the standards of his presidential office include defending white nationalists, attacking prisoners of war, abusing the use of emergency powers, personally criticizing federal judges and much more.
Norms are perceptions or beliefs about what we understand the rules for acceptable behavior to be. They are powerful predictors of behavior. By openly broadcasting his anomalous actions and views, Trump is shifting public attitudes about what is deemed appropriate – not only in politics, but also in society.