Perhaps he needs to look further back to understand that Nazis and Communists are two sides of the same coin.
Nazism developed from many threads, including German militarism and 19th century anti-Semitism, a major dread of Bolshevism (which they saw as a more or less Jewish phenomenon), the political/economic loss of WWI before a complete defeat in the field (which Nazis blamed on leftists/communists), the very real efforts of the USSR-directed communist Internationale to spread revolution; the Great Depression and economic consequences of the peace, etc. Operationally, much of the Nazi program was lifted from Stalin: concentration camps (modelled on the GULAG); mass propaganda; suppression of national groups; internal colonization and Russification; State capitalism; massive public works projects; large para-military and secret police forces; locus of power in a single Party rather than the government; genocide; militarism; expansionism; pervasive police supervision of society; brutal suppression of internal political enemies; etc. Somehow our contemporary lefties omit all that.
Everything you say here is spot on. There was a quote posted a while back here on FR written in the New York Times circa 1925-ish. I want to say it was Goebbels, yes the Nazi, who stated (paraphrase) that there was not a dimes worth of difference between the Commies and the Nazis.