The answer is so simple most people don't believe that its true.

The Republicans....i.e Prescott Bush and Roland Harriman and their henchmen the CIA.

Nixon who was hand picked by the two was viewed as a slam dunk winner prior to the 1960's election.

It was one of the closet elections in our nations history and Kennedy was helped out by having the Frankie boy solicit notables to vote for the democrats.

The reason is two fold and fairly obvious.

1. Don't cater to Mobsters then have your brother go after organized crime once you get into office, thinking your impervious to retribution, i.e. Jack Ruby

2, Don't cancel the bay of pigs, the private little business operation of the CIA, i.e. Bush and Harriman and don't think that their Skull and Bones club won't come and kick your ass.