I'm not disagreeing with you; I'm just asking you to cite one or more of these accounts describing his lack of intellectual stamina.

This account [1] by the ghostwriter who wrote 'Art of the deal', who spent months with him, suggests that he is neither smart nor patient. Over his long life, starting with a very silver spoon that he wasn't able to destroy, he effectively focussed most of his energy to coming up with a couple of heuristics for making deals and communication. I get the impression he spent most of his life's effort on something that might be called 'social hacking' here.

[1] http://www.newyorker.com/magazine/2016/07/25/donald-trumps-g...