Trump has lied for so long and so often he no longer can tell the truth from a lie. If you actually took the time to listen to him and read what he has said about himself the fact that he lies would come as no surprise. He has often stated that lying is a major part of his business practice and, as is obvious, he has brought the same standard into politics. Trump has bragged about intentionally lying to leaders of other countries, his own supporters, and, of course, the news media. He knows that if you tell the same lie long enough people start to think it is the truth which is what he said he has done with the media in an interview he gave.
The amazing thing is the gullibility of his supporters since he has admitted lying to them on many occasions yet they still believe what he says. He call Hillary a liar yet she told the truth 3 times more often during the campaign than Trump did.