I study liars. I’ve never seen one like President Trump.

In research beginning in the mid-1990s, when I was a professor at the University of Virginia, my colleagues and I asked 77 college students and 70 people from the nearby community to keep diaries of all the lies they told every day for a week. … One category of lies was so small that when we reported the results, we just tucked them into a footnote. Those were cruel lies, told to hurt or disparage others. … An astonishing 50 percent of Trump’s lies were hurtful or disparaging.