The President wanted to use a 2 seater fighter, but the Secret Service said no, that he would have to use a plane with at least 4 seats, so that 2 of his Secret Service personnel could be with him.
Actually there was only one US Secret Service agent on board. The fourth seat was filled by Naval Aviator Lt. Ryan Phillips.
A wise choice, I must say. More important to have a second type-certified pilot aboard than another federal police officer.