I agree on the ear thing, but not that it's a very difficult shot, that's simply not true. A man standing in one spot is not counted as a moving target either. This guy is shooting at 770 yards with an AR-15 in strong wind and it's pretty precise. Realize that there's a lot of variables here of course.
A 2.5cm by 2.5cm (1 inch by 1 inch for my colonial cousins) is a very small target at the range they quote.
Moving your head while talking will move that tiny target by more than it's total size often and irregularly.
Add that to the adrenaline going through your system as you attempt a shot on a president in view of the public, press, and counter snipers of the USSS.
It isn't happening, outside of bad fiction.