Many member of the JFK's Secret Service detail were complicit in his assassination and it has been alleged Landis was one of them. Secret Service agents are highly trained to protect the President's life at any cost.
Specifically, they are trained to pounce on top of the President to protect him if he is caught in the line of fire. In other words, they are trained to jump on top of the President to shield and protect him. When JFK was shot, ZERO Secret Service members attempted to do so including special agent Roy Kellerman, who was riding shotgun in President Kennedy's limousine. Mark Lane pointed out in his book, Last Word that Landis also completely failed to attempt to protect President Kennedy in any way:
"On November 22, 1963, Landis was standing on the running board of the follow-up car, not far from President and Mrs. Kennedy. He had an excellent view of the effect of the bullets upon the occupants of the vehicle. Since the presidential vehicle had stopped, some witnesses say 'almost stopped', after the first shot was fired, he (Landis) had several seconds after the first shot was fired to attempt to cover President Kennedy and his wife with his body. He never moved."