I am hoping someone can help me remember the name of a 1970's science fiction short story (maybe a novella) about the JFK assassination. What I remember most about the story is that it loops back on itself, so that at the moment the fatal bullet strikes, Kennedy finds himself back at the beginning of the motorcade--or maybe the beginning of that day. I used to read a lot of Harlan Ellison, but I know it wasn't one of his stories. Not much to go on, I know, but I would be grateful if anyone can help me track down the story. Thanks!
Could you be thinking of J. G. Ballard's "The Assassination of John Fitzgerald Kennedy Considered as a Downhill Motor Race"? I don't believe it loops, but it is connected to Ellison in that Ballard submitted it for 'Dangerous Visions', but the agent (who found the story appalling) never forwarded it to Ellison, causing some friction between the authors. It later became part of Ballard's "The Atrocity Exhibition".