A Paul Krugman column well worth reading. From the article:

Why does Trump keep repeating what even he has to know by now is a flat lie? I suspect it’s a power thing: he enjoys showing that he can lie repeatedly through his teeth, be caught red-handed in his lie again and again, and his followers will still believe him rather than the “fake news” media.

https://krugman.blogs.nytimes.com/2017/10/14/lies-lies-lies-lies-lies-lies-lies-lies-lies-lies