Can you Change the Past?

Another answer would be just to deny that you can’t change the past. So, I go back in time, and put a flying tackle on Oswald, sparing Kennedy from death (assuming there was no one on the grassy knoll that really did the dirty deed). But because of some decisions by Kennedy, I end up dying in 1991, which means I never get to go back and save Kennedy, in which case Kennedy dies, in which case I live and go back to save his life, in which case he lives and I die in 1991, which means that I never get to go back…….