Trump lies because he’s done this his entire career and never been held accountable for it.
Now he’s in front of the entire world, where he has people who will actually hold him accountable for the things he says, and he does not know how to process that, because its not in his character to do so.
He’s been a liar his entire life! He’s a BS artist! And when he gets backed into a corner, then his default is to lie, make something up, deflect and divert, and when people call him on it, he says “fake news.”