In the field of psychology, the Dunning–Kruger effect is a cognitive bias in which people of low ability have illusory superiority and mistakenly assess their cognitive ability as greater than it is. The cognitive bias of illusory superiority comes from the inability of low-ability people to recognize their lack of ability. Without the self-awareness of metacognition, low-ability people cannot objectively evaluate their actual competence or incompetence.

As described by social psychologists David Dunning and Justin Kruger, the cognitive bias of illusory superiority results from an internal illusion in people of low ability and from an external misperception in people of high ability; that is, "the miscalibration of the incompetent stems from an error about the self, whereas the miscalibration of the highly competent stems from an error about others."

Welcome to the age of the Dunning–Kruger president!
He just declared that he's better than Reagan, which anyone aware of Reagan knows isn't saying much at all, but it's still delusional, at least in Trumps case.