“the reincarnation of JFK (who was never that popular while president)”
To be perfectly blunt, getting his brains blown out was the most popular think JFK ever did.
Having barely one one of the tightest elections in history, but with hindsight being 20-20, it is hard to find anybody who will admit to having voted for Nixon over JFK.
The media was all over the Kennedys after the election. Kind of like today, except they were better dressed. The media created Camelot and the assassination made him a martyr.