Not all con(fidence) artist have an MBA. But they instinctively know how to recognize and exploit weaknesses in their victims. Sort of along the the lines of a used car salesman.
Once the deal is signed (as in the presidency) we are no longer any use to him or his bank account. The hook has been set.
I also have an MBA and 'use and abuse' was never part of the curriculum. The psychology I learned and have always used as a good business practice was to be ethical and create return customers as a means to successful growth.
Perhaps Trump's 'eat or be eaten' world of real estate has turned him into the snarling creature we see before us ~ one who judges everybody by his own low standards ~ but a truly smart man would be able to adjust from real estate to politics which, admittedly, is equally as treacherous. The difference being, of course, that he can't just say "screw you" and walk away from it as he does with his 'swing and miss' business failures.
Trump is not a smart person ~ he's cunning. His persona as a successful businessman is a veneer. Underneath it all lies the heart of a viper in camouflage with a laser beam on his next victim.
Even if his base isn't sophisticated enough to see through Trump's veneer, his counterparts around the world recognize him immediately for what he is and are wisely on guard.