First, this will contain a spoiler (not a huge spoiler, and not one that's really all that important to the novel, but a spoiler nonetheless) -- so if you haven't read the novel and don't want to know anything about what happens, please read no further.
King makes the decision in 11/22/63 that Lee Harvey Oswald was a lone gunman, shooting three times from the window of that book depository on Dealy Plaza in Dallas. Oswald fired three shots, says King -- the first one did not hit the target, but the second two did. No second shooter on the grassy knoll. No "magic bullet" that had to change direction in mid-air. No CIA, no mafia, no Cubans, no LBJ, no Communists. No conspiracy. Just Oswald.
I bring this up because I read recently that almost 80% of the American public believes that some sort of conspiracy was involved in the assassination of JFK. As few as 12% accept the Warren Commission's conclusion that Oswald acted alone. I know that when I first heard about this novel I wondered how King was going to deal with the events of that fateful day. King includes an afterward in 11/22/63 explaining that he is now convinced that Oswald was the lone shooter.
Does this effect your enjoyment of the novel? Will the 80% who are sure of a conspiracy feel cheated? Or is it all a moot point, since the novel is much more about protagonist Jake Epping than it is about Kennedy. But there IS all that history . . .