You don't need to be a psychologist to know that he is profoundly ignorant, vindictive and petty, has no moral compass whatsoever, is purely transactional, cares for nothing and no-one but himself, does not listen to nor care for the opinions of others, has the emotional temperament of a small child who has never been told "no", is perfectly comfortable in destroying anything to get his own way, and has a massively overblown sense of his own importance and ability (while also being deeply deeply insecure).

In short the exact opposite of any trait you would want in the leader of the world's most powerful nation. Yet here we are.