Have you ever read any of these science fiction stories where the characters decide to travel back in time to stop Hitler? (Latest in the genre: the DOCTOR WHO episode “Let's kill Hitler")
Well, then, guys, you have a shot, and you don't even need a time machine.
If you don't believe me: GUARDIAN headline: Donald Trump says he would encourage Russia to attack Nato allies who pay too little. Some people should not, under any circumstance, be allowed within feet of the Presidency. This is not hard, it is easy.
Again, no time machine required.