physical examination

Hillel was an ancient Jewish Talmudic scholar becoming the President of the Sanhedrin, the ancient Jewish “Supreme Court.” He was asked one day to teach a possible convert all of the Torah while the applicant stood on one leg. You can find what he said in the footnote [1]. My purpose in mentioning the story is only to introduce the idea that we can learn much from standing on one leg.
With President Trump's annual physical looming, what matters most? And specifically, what would it take to make a president unfit to serve?