I'm old enough to recall that brouhaha.
Some time in the past three or four years I read that President Kennedy more or less pulled that comment, to the effect that any fit, red-blooded American lad should be able to hike 50 miles in a day, out of his, let's just say, 'hat'. After all, that's roughly a double-marathon, and it's well beyond any ordinary fitness level in the industrialized countries.
The media picked that up made such a fuss about it that he forced his kid brother RFK to do one - to prove his point. It about killed him. (JFK, of course, could not have hiked 50 miles in a day to save his soul.)