Kuvult, many good points.
> no one had any idea about a Holocaust in the 1930s
It was already clear that the 20th century is different. First WW1 (aka at the time as a Great War) with unheard of losses in “developed” world. Then, by this time, millions of Jews, as well as non-Jews, died or/and suffered immensely in USSR and threatened other countries already.
I agree that association of Jews with communism was not helpful to obtaining US visas and might have contributed to immigration restrictions of 1920s in the first place. We see in our time how nativism strengthens from what they see in the arrivals. This association also added to Germans conflating Jews and Communists.
Furthermore, before demanding prophetic vision from FDR, we should look at our own leaders who were often similar blind of the upcoming danger. FDR might had better military intelligence, but Torah wisdom should not be less than that …