It's not that amazing if you think about it.

Back when WW1 ended, a lot of Germans and Austrians kept the firm belief that the wars fault lied entirely on entente's side and Austria and Germany were mere victims.

There are always people who are going to refuse to believe those things happened; either because "no true German would do that" or because if they believe that would mean their ideology is tainted, or any among a thousand other reasons. There are always people who deny.

And on this specific scenario, where a nation managed to conquer almost the entire continent, nationalism takes a big role. Just as Greeks remember Alexander and the French remember Napoleon and Italians remember Julius Caeser, the Germans would remember Hitler.

So, that's the prescience of Eisenhower: Hitler and the Nazis must had not become a hero for the Germans and the way to do it was to never let them forget or deny what hitler and the Nazis did.