Not quite. The assassination of JFK succeeded, but remember how Jackie O was scooping up parts of his skull and brains afterwards and everyone assumed she was in shock? It was actually part of the training that she received from the OSS, to be used in just this very situation.
The reason? JFK was about to undergo the first reanimation surgery performed on a public figure, right there in Dallas. Yes, the OSS had figured how to bring the recently deceased back to life. Some say they used a genetically modified version of Rabies, others that it was a combination of plant extracts commonly used by the Legbo of Western Africa and Haiti. No one will ever know for sure, because the surgery did not go as planned.
This was a very experimental surgery, and it appears that the combination of the violence of his death and missing brain matter caused the newly reanimated corpse of JFK to rampage through the lower floors of the underground emergency bunker that future president, George H.W. Bush had built with the money he made as President of Zapata Off-Shore Co., an oil concern. His gracious donation reportedly in no way affected his future appointment as CIA Director, Vice Presidency or election as President.
Shambling amok in the facility, JFK's newfound hunger for flesh became a secondary concern to what was happening to those he attacked. Shortly after being bitten or scratched, the attacked person would exhibit signs of massive infection and appear to expire yet once expired they would become a gruesome echo of what our once young and virile president had become. After a series of these "infections" as the scientists began to call them it was found that, ironically, a bullet to the head would put these "Walkers" down.
A short, but tense battle ensued and the bunker was reclaimed by the living. The problem now became that no one could agree on what do with the former president. Scientists wished to study him, military men wished to use him as the basis of a super-soldier, and PR wonks wanted to trot his shambling corpse around to steel our nation's resolve - that even in death, America will persevere. It was all for naught - his cell was empty. It was determined that a private security firm employee named Jim Jones was missing as well as well as an Apache helicopter and 10 lbs of cyanide.
Tracking the helicopter to French Guyana it appears that Jim Jones was using what used to be JFK as the central component of his previously undiscovered cult's promise to live forever. He was to sacrifice his poisoned congregation to JFK, who would feast on their flesh and subsequently reanimate them. Who knows what the death toll could have been if the CIA hadn't stopped this horrible scene in its tracks by immediately executing the cult members regardless of they were dead or alive. You simply couldn't be sure.
TL; DR: Undead Kennedy