In all fairness, most of the awareness of what happened in Europe only coalesced after the war. America was in the throes of the Great Depression, and European news was minimal, mostly from Britain, and limited to newspapers.
For their part, the Germans had tried in several ways to kick out the Jews, but other countries were not interested. Even at first, “concentration camps” was such a neutral term that the US used them during the Philippine Insurrection.
For their part, the Germans can claim early credit for “extermination camps”. The Germans used concentration camps in German South-West Africa during the Herero and Namaqua Genocide between 1904 and 1907. The camp at Shark Island, Namibia was of the nature of an extermination camp.
However, some of the WWII German camps were slave labor, not extermination camps. Still reprehensible, but many of those activities were not widely known in the US to long after the war.
Can you imagine if the world had had the Internet for communication back then? Wow.
Despite what the general American public might have known, Franklin D. Roosevelt and his administration, especially his State Department, knew early enough about the severity of Nazi war atrocities to potentially save the lives of many European Jews. But their record in this area was abysmal. There were numerous missed opportunities, some deliberate.
So the author of the posted piece is correct in naming Roosevelt as a malfeasor in what we now refer to as the Holocaust.
This sad history is recounted in a book titled "While 6 Million Died," written by Arthur D. Morse in the 1960s.
Yet these later revelations about Roosevelt et al did little to relieve too many American Jews from their addiction of voting for Democrats.