You know what most time travel scenarios seem to involve? Going back in time and killing Hitler. Someone always posits the whole “kill Hitler” thing. That’s how I know there’s no such thing as time travel: Hitler didn’t die before he caused any problems.
But then there’s the life saved, like John F. Kennedy. Stephen King wrote a book on a guy who time travels back to save Kennedy, and Hulu has a mini-series for the adaptation of that book coming in February. Teaser after the cut.