He's hardly "great" at much, just pretty competent at his niche of appealing to the lowest common denominator, and at the right moment in history when the GOP was going long with minority demographics he makes the perfect short play with white nationalism.
One cannot make a serious diagnosis of Trump no matter who they are because they haven't done the workup. Speculate away, but we can't know. His health seems to be an issue because he could not walk 700 yards and he had trouble keeping up with the schedule he set for himself. Lack of physical activity and poor lifestyle alone can hasten the natural effects of aging all on its own. Take an individual like that and place him or her under the spotlight and the condition is magnified by stress.
I'd leave a specific diagnosis to a highly trained specialist after proper testing and evaluation. I wouldn't touch this with a ten foot pole.
Well, it's safe to say a lot of his problems are self-inflicted: he actually thinks exercise is bad (it'll supposedly shorten his lifespan), he has a terrible diet, and he only gets a few hours of sleep every day. At 70 that's a pretty volatile cocktail of decisions, and that's not including the stress of his first job where people are genuinely allowed to tell him "no."
Then there's what we've already observed in this thread: that his language is becoming simpler and increasingly muddled. That doesn't necessarily mean dementia, but combine it with his poor lifestyle and you wonder how much longer he really has. Never mind whether or not he'll be impeached before 2020... will he survive until 2020?
But stamina he has it. The best stamina. Only he has the stamina to be president.
Trump is President, right? Nearly 63M people voted for him, correct?
And yet he's completely unfit to lead this nation. He's running the most successful scam in the history of the world.
My opinion stands.
I also do not agree with your opinion that Trump talks to his base as if they are dumb. This would dovetail directly into my statement of underestimating your opponent.