Here is Arlen Specter demonstrating his Single Bullet Theory, but note that he's got it wrong.
The trajectory of the bullet had to be from right to left, not left to right. What he is proving there is the impossibility of the Single Bullet Theory.
Of course, his successors scrambled to save it by claiming that Connally was placed very much inborn of Kennedy, unlike what we see above. But, was he? A little, but not much.
Connally could easily place his elbow on the ledge of the door.
Here it is closer up.
But, the point is that this is all wrong:
And he's the guy who thought of it. His reward? He got to be a US Senator. Do you know that he ran for President in 1996? Just imagine if he had won. He'd have been the 5th person with blood on his hands from the JFK assassination to become President of the United States, after Johnson, Nixon, Ford, and Bush.