some of them are in the "outrage" territory by any reasonable meaning of the term, like for example the Katyn massacre coverup or the Operation Keelhaul.

Agreed, but keep in mind that the British, not the Americans, played the largest role in Keelhaul, such as rounding up the prisoners and deceiving them. And most of them, such as Lord Forgot-His-Name, who betrayed the White Cossacks (look it up), were hardly left-wingers - just scumbags.

(Generally speaking, Churchill, despite being extremely cynical and loathing Stalin, in practice made more concessions to him by way of appearsement and realpolitik than Roosevelt's administration ever did - for all its supposed naivety and/or Communist sympathies)