Yeah, that hindsight kicks in for some. The allies were on the run in Europe until we jumped in, so exactly how fast could something have been done. As one who studied the war for years I am amazed it went a quick as it did. Luck and stupidity in Germany played in as well. And yes saving the Jews would never have played that well in the US. Then the photos came out and the issue became real.
You hit on it, I believe the main reason why the Shoah stands out from the other Holocausts, besides the sheer numbers, are the images that have been seered into our collective consciousness. The Nazis were so proud of what they were doing, they had the audacity to film the atrocities, and they, being Germans, documented everything.
The Soviet crimes were for the most part committed out of sight.