He's not dumb! He is a narcissist and therefore has to be right about everything..that's his weakness and his strength, as it also drives him to succeed. How many wise wealthy people have you been around? Their not all the same and have different backgrounds. In fact, I think Mark Cuban acts like a dumb ass...can't stand the guy, but I know he's smart!
Trump has a "New York" attitude and combine this with a narcissistic disorder and you get a very competitive person. Is it difficult for you to understand that he is serious, focused, and logical when he has to make important decisions in private settings? Even though "The Apprentice" was a T.V. show, he took it very seriously when dealing with conflict management...big egos...and did it very well.
You assume so much when it comes to his business practices! However bad it it could be, it could never compare to a corrupt "sworn in" elected official who steals from the PUBLIC!