I'm not even sure ability is the issue when it comes to grasping things.
I think it is simply he chooses not to understand in favor of gut instinct and even what he last read / saw on TV.
Like you said I don't want to go down the rabbit hole, but I think there's a difference between trying an unable and simply choosing not to try understand a thing (for whatever reason that is).
> I'm not even sure ability is the issue when it comes to grasping things.
I am pretty sure it is lack of ability. Some of the reported interactions between him and other world leaders is pretty alarming. For example, Merkel of Germany had to tell him 11 times that he could not negotiate trade deals between the United States and Germany because Germany is part of the EU. (http://www.businessinsider.com/trump-trade-merkel-germany-eu...)
He uses his gut instinct all the time because that is all he has.
I think it is simply he chooses not to understand in favor of gut instinct and even what he last read / saw on TV.
Like you said I don't want to go down the rabbit hole, but I think there's a difference between trying an unable and simply choosing not to try understand a thing (for whatever reason that is).