Franklin Roosevelt’s worst decision was Executive Order 9066, “Authorizing the Secretary of War to Prescribe Military Areas”, which is to say, interning Americans of Japanese descent.
The decision for internment had nothing to do with intelligence (particularly, as often alleged, from MAGIC cables) and everything to do with the conviction that “a Jap is a Jap,” as General John DeWitt said. I’ve never been very happy with historical explanations that start and end with “it’s racism,” but really … it’s racism. You can tell of course because there’s no similar simultaneous effort against Americans of German descent. You can tell because of Japoteurs and “Slap the Dirty Little Jap” and lots of other examples.
For my family, the war was the European war. My grandfather, a German-born American, had no trouble the way Japanese Americans did; he flew a bomber for the US in the war. We had the luxury of remembering the war the way white people often do – without considering how much better we’ve had it because of our whiteness.
It’s profoundly difficult to integrate the psychology of the Pacific War and the European War for the US, either when considering them from the standpoint of history or of memory.