For a person who has relied on telling lies for everything he has done, Donald Trump is surprisingly bad at it. He has a habit of going over the top and over-compensating, like when he recently denied being a racist. It would have been perfectly fine to simply say "No, I'm not a racist", but he had to add "I'm the least racist person you've ever interviewed". Being "the least racist" doesn't even make sense, but he feels compelled to brag about being the best at everything.
He also has plenty of verbal tells for when he is telling a lie. He interjects "believe me", "I can tell you", or "it's true", as if he knows the lie is too transparent to stick. A person telling the truth doesn't feel a need to reinforce his statements all the time.
To be even a mildly succesful habitual liar, you really need to be better at hiding and covering up your lies than what Trump is showing at the moment.
