I was the only one who had a chance to do anything,” Clint Hill said. “The way everything developed, the way all the other agents were positioned, I was the only one who had a chance to get to the car and do anything.

Mr. Hill dove onto the presidential limo in a heroic attempt to save President John F. Kennedy when he was assassinated in Dallas in 1963.

Clint Hill, the Secret Service agent who leaped onto the back of President John F. Kennedy’s limousine after the president was shot, then was forced to retire early because he remained haunted by memories of the assassination,