Things were not quite as simplistic in all respects and all regions as you seem to think they were.
If you think I'm too "simplistic," do you want to suggest an example, where the US supported our Axis enemies against our Communist allies?
I think the key point to understand is that America's strategic alliance with the Soviet Union was made by Roosevelt and supported by Churchill with far fewer reservations than we today believe appropriate.
So, both the credit for victory and blame for Communists' successes go to FDR.
But, in Rooosevelt's defense, please remember the basic wartime statistics: for every German soldier Americans killed, the Soviets killed ten. And for every American soldier who died in battle, 100 Soviets died.
So in the end, it was largely Soviet blood with American treasure which won that war. And I don't think we should be so quick to forget it.
As for Communist spys in the US government -- yes, all of that is true, and all rightly blamed on President Roosevelt. The US government did not really begin to understand that Russia would be the new enemy until after FDR passed away, in 1945.