That makes me think of the Simpsons vignette "Time and Punishment" since it involved repeatedly traveling back to the same point in time. Of course it was a parody of Ray Bradbury's "A Sound of Thunder," but in Bradbury's story it wasn't possible to visit a point in time that had already been visited.In 2011 Stephen King wrote a time travel book set in contemporary times entitled "11/22/63" and yep, it's another JFK must die story.
Aside from being about JFK, what I found intriguing in this story was King's time travel premiss. The way he had it, the protagonist would go through a time portal that just existed, no time machine. This portal was permanently fixed in time; that is no matter when you go through, it's always to the same date in 1958.
So if you go through the portal to 1958 and change history, return to the future and don't like the change, all you have to do is go through the portal again to the same date in 1958 and everything is reset and what you did before is undone.
So when the hero decides to save Kennedy, it means he has to wait five years from 1958 to 1963 to save him, making a life for himself in the Dallas area while he waited.
After finally saving Kennedy, the hero returns to his own time to find things are much worse. But all he has to do is go back to 1958 again and everything he did in those five years is erased and his contemporary world is back to normal again.
Robert
Kor