He's a narcissist. Of the clinical kind. If you have ever dealt with one of these you'll find that the truth is irrelevant to them. They do everything solely to support and promote their self image.
I wouldn't call him dishonest in the sense of a person who knows what the truth is and lies about it is. I think Trump thinks he's telling the truth. He's more of a "if it feels true, it is true" person.
