In Liberal Fascism, Jonah Goldberg argued that fascism was an outgrowth of early 20th century left liberalism. Reviewing two books about Pius XII for the Spectator, Pope during World War II, historian Andrew Roberts writes about --
the discussion that took place between Roosevelt and Cardinal Eugenio Pacelli at FDR’s upstate New York home, Hyde Park, in 1936. According to the President’s recollection in 1943, the future Pope — then Vatican secretary of state — had said that the United States was ripe for a Communist take-over. FDR disagreed, saying that in fact the genuine peril was of America going Fascist. ‘No,’ said Pacelli. ‘Yes,’ said Roosevelt. ‘Mr President, you simply do not understand the terrible importance of the Communist movement,’ said Pacelli. ‘You just don’t understand the American people,’ FDR claimed to have replied.
This book also makes the plausible case that in the Twenties, Pacelli originally ‘saw Hitler’s Nazism as merely a political ruse. Aware that Hitler’s earliest ostensible political alliance was with the German Workers’ Party in 1919, Pacelli remained suspicious of Hitler as a politician of the left.’ He certainly told the US consul in Cologne, as late as 1939, that Hitler was not a true Nazi and that he ‘in spite of appearances would end up in the camp of the left-wing Nazi extremists where he began his career’.
Jonah reads this as: Pius XII thought that Hitler was a man of the left, therefore I am right to think of Hitler as a man of the left. The problem is, as Roberts notes, that Pius XII's assessment was the essence of his miscalculation about Hitler and his resulting ineffectiveness during the Holocaust. FDR -- one of the targets of Liberal Fascism -- understood that Fascism was a pernicious philosophy on its own terms, and very different from Communism.