JFK and Nixon were good friends when they were both in Congress, IIRC.
Nixon apparently believed in looking out for his friends, even unto his own destruction.
Nixon and JFK worked closely trying to rid the nation of communists, and they were unified in their complete distrust for J. Edgar Hoover. Nixon viewed "enemies" as people who had tried to harm him personally, he did not consider partisan political rivals to be enemies unless they attacked his character.
Joe Kennedy held Richard Nixon in high regard. They were friends at one point.