There's an interesting theory that Hitler was put in place by time travelers as the last-bad option that wouldn't destroy the timeline.

Hitler (and Trump) made a number of blundering errors that any idiot should've/known better than to make. Had a competent, or even a supervillain-type been in charge, things could've turned out even worse than they did. You don't have to look far- some of these villains attach themselves to those in power. Himmler and Heydrich would've been far worse for the world, but were somewhat limited by not being the ones directly in power.