One of his preferred "gurus" is a guy who pushed one of those self-help bullshit "if you just believe hard enough, you'll manifest your desires!" proto- The Secret frameworks, and he does appear to operate that way—strident bluster, declaring defeats and "white peace" as unqualified victories, willfully ignoring inconvenient facts, all that stuff. Like, look at the totally-bizarre sharpie incident in his first term, for a trivial but illustrative example.

However, it's worked out well for him personally (less so for those he does business with, or near, or for the US...) so despite being on-paper delusional, I admit the waters are rather muddied.

https://en.wikipedia.org/wiki/Norman_Vincent_Peale#Influence