What was the US response to evidence that there was a "holocaust" being commited against the Jewish people during WWII?
The first US response to early reports of the Holocaust was to try to keep the issue out of the public eye. The Holocaust is often seen as starting with the Wannsee Conference that set out the plan for the "Final Solution." This was in January of 1942. That fall, the US government received reports from Europe about these plans. They did not announce the report and asked Jewish organizations that had received it to refrain from announcing it as well. The President did not feel that it was a good idea to make this public because he did not want to make the public feel that all Germans were in favor of the killings. He was, at that time, hoping that some Germans would rise up and overthrow Hitler and thought that the report would discourage that.
Later on, the US also decided not to bomb extermination camps like Auschwitz. They were very ambivalent about that decision because they wanted to stop the killing but were not at all sure that bombing was the best way to go about it.
It must be noted that Jewish groups at least acquiesced in both decisions. This may not mean that they totally agreed with them, but it does at least mean that they were willing to accept them. This tends to argue that they did not think the actions (or lack thereof) were evidence of anti-Semitism.