“Marksman” is the lowest qualifying rate for a shooter in the US Military. It’s followed by “Sharpshooter” then “Expert” which means Oswald barely qualified with the issue weapon after weeks on the range.
If Oswald was truly the lone gunman, why wouldn’t he shoot Kennedy as he was driving slowly towards the book depository or when Kennedy was directly underneath him. Those are much easier shots, than a shot at a vehicle driving away from him
Finally, More than likely,the first shot would be the most accurate as the shooter would still have the element of surprise and not rushing to get the shots off and make the escape.
As far as shooting at Kennedy at the distance he did it would seem to me he would have had a better line of sight as I believe the traffic light at that corner was a bit of an obstruction to a line of sight.
Thart award of Marksman is at 200 yards over open sights. The head shot for Kennedy was at 68 yard. Witha scope.