I saw a show a couple of years ago...think it was the History Channel.
They created a duplicate of the whole shooting scene.
and a shooter using the same gun and a similar car with dummys in it. The shooter was an expert I *think*, but said the shots were not dificult.
The shooter had the same angle and view as in the original event and the car traveled the same path at the same speed.
The shooter was easily able to hit the "president" at least 3 times, over and over again within the time interval of the orginal shots.
He even stated that the going away shots were the easiest as the target was stable, traveling pretty much in a straight line and going away, requiring little effort to hit.