I read recently that JFK was attempting to engage in marital activity with a woman not his wife at the White House pool a few weeks before the assassination. In the process of being rebuffed, he injured his back, causing him to wear a back brace for support. Where this ties in to Nov. 22 is that if you look at the Zapruder film, when JFK is first shot through the throat, he does not fully slump over; the back brace he is wearing is holding him up! This left him in perfect position for the head shot, which killed him.
That account was given in Seymour Hersh's, The Dark Side of Camelot. While not necessarily the most credible of writers, this book is one of his better documented pieces.
I doubt he was ever "rebuffed", unlike Clintoon.
And on 11-22-63, Kennedy was probably wearing a bullet-proof vest. Since there were at least two excellent marksmen that day, the vest didn't do him much good.