Pearl Harbor
Nobody wants to think that FDR allowed Pearl Harbor to happen either, but he did. What is more, there is good evidence that FDR not only allowed it to happen, but more chillingly, that he provoked the Japanese into attacking with a carefully calculated series of moves.
Granted, the Japanese were already storming around in Manchuria and Indochina prior to Dec. 7, '41, and there were very good reasons for the United States to enter the war against the Japanese and especially, the Nazis.
Nevertheless, the sacrifice of several thousand Americans was wrong, no matter how you look at it.
S