Old Gumlegs (as W.C. Fields referred to him) was a socalist, so he saw no problem with a Communist. It was the next stage up! FDR ranks as one of the worst Presidents in history IMHO. Made the Great Depression worse, knew about the Pearl Harbor attack in advance and sold out his country to the f-ing Russians and socialism.
There uncomfortable fact about a lot of leftists is that they saw the USSR as an "interesting idea." Some seemed to take a more reaslistic view. I divide American liberalism between folks like HArry Truman, who were big-government progressives, and John Kerry/Hillary Clinton/Moveon.org, who are aggressive cultural Marxists and want to remake American society in their own secualr humanist image. To the latter group, it's like a religious calling.
I regard FDR as somewhere in between, if that's possible. He was just ambivalent about Communism.