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As an aside, I had read the allies didn’t bomb the railroad lines because they knew the nazis would blame Jewish deaths on those bombings rather than on the camps they ran.
It's not very relevant to the topic, but the answer is "unclear", as far as I remember.
On one hand, as soon as Nazis started killing the Jews in the Soviet Union in the summer of 1941 there was plenty of information filtering to the allied forces. It was primarily stuff like German police reports intercepted by British intelligence; local eyewitnesses, escaped Jews, Soviet news sources etc. By 1942, detailed reports on a Nazi plan to murder all the Jews (with details on methods, numbers, and locations) have certainly reached the Allies from source like Warsaw ghetto underground, various eyewitness account etc. In fact, in 1942 the Allies issued a proclamation condemning the “extermination” of the Jewish people.
On the other hand, it's unclear if this intelligence was ignored or simply misunderstood. The shock of the US and other Allied commanders who liberated camps at the end of the war might mean that either that information was not shared from up high or the extent was not understood.
In short, the US could have done something, from accepting Jewish refugees when it was still possible to escape to actually bombing the railroad lines in the late stages of the war. Same goes for other genocides that the US, a predominant military power "committed to the good" has completely ignored since then. To name the few recent ones, Rohingya, Dafur or Rwanda come to mind.
As an aside, I had read the allies didn’t bomb the railroad lines because they knew the nazis would blame Jewish deaths on those bombings rather than on the camps they ran.