Choosing the narrowest intervention in Hitler's rise

If you could intervene in history, when would you stop Hitler's rise?

The narrowest point would be after his electoral failure but before he turned the Nazi Party's parliamentary strength into power, though the consequences would remain uncertain.

Removing Hitler would leave the course of German politics uncertain, including the possibility of another Nazi leader taking his place. The proposed intervention falls between electoral disappointment and his use of the party's parliamentary position to obtain power. New elections might then weaken the party enough for it to fall apart. That result depends on a very narrow choice of timing and remains a possibility.