Donald Trump lies a lot. To be a successful liar, you need to be smart, have good memory and be able to sort of half believe your own lies while you are telling them, to make your body language say that you are telling the truth.
Donald Trump is not smart, and his memory seems to be working so-so. To make matters worse, he goes all in even on small and insignificant lies, which has quickly destroyed his reputation.
Somewhat surprising for a habitual liar, when he is lying he has plenty of tells which can be picked up on fairly easily by anyone. When Donald Trump says "believe me" or "it's true", you can safely assume that he is lying. His calling anything "fake news" is a pretty strong indication that the story is true, and embarrassing (incriminating) for him. Having such strong verbal tics makes you a very ineffective liar.
Donald Trump can't even lie properly. USA is run by a fool.
