(Asking on behalf of an anonymous person on the internet whose mention of the comic piqued my interest -- so unfortunately, I cannot offer any more details.)
[...] A comic where someone goes back to kill Hitler and it results in an actual 1000-year Reich, because although he successfully killed Hitler, the Nazis got hold of the laser rifle the assassin had brought back with him to do the job. So, another dude gets sent to kill that dude, but that doesn't work out either, so another dude gets sent, then another, then another....
I must have read it in the early 1980s or so, but it could easily have been a story from earlier [...]
