Three features of the old Left's racism feel contemporary. Naturally, Communists could not say that Jews were members of a "Judaeo-Bolshevik" cabal. They had to recast the conspiracy as a right-wing plot and substitute "Zionist" for "Jew". When Stalin put Rudolf Slansky and other Czech Communists on trial in 1952 the authorities announced: "The whole worldwide Zionist movement was in fact led and ruled by the imperialists, in particular the US imperialists, by means of US Zionists. For US Zionists, who are financially most powerful and politically the most influential Zionists, form part of the ruling imperialist circles of the USA."

Rudé Právo, the organ of the Czech Communist Party, said that Slansky and his co-defendants were "Jewish cosmopolitans, people without a shred of honour, without character, without country, people who desire one thing — career, business and money". Communists and their supporters imagined a vast Zionist conspiracy reaching from the US Supreme Court to Tito's anti-Stalinist supporters in Yugoslavia. For all that, they maintained that they were not anti-Semites but enemies of Zionism. They might have been modern "leftists" talking about the "Israel Lobby" conspiring to organise the Iraq War of 2003, while all the time insisting that there was nothing remotely racist about their conspiracy theories.

The dog days of Stalin also saw a new loyalty test for left-wing Jews, many of whom did not consider themselves remotely Jewish. My grandfather, whose parents had fled to Britain from the pogroms in Lithuania, abandoned his religion and all connections to Jewish culture and became a Communist, as Lenin would have wanted. Objectively, there was nothing Jewish about him. But men like him, who had gladly broken free from their old religious and cultural identities and spent their life serving the party, saw the party use their ancestry to damn them. In Czechoslovakia, any Jew was a suspect. When the secret police imprisoned Artur London, deputy Foreign Minister in the Slansky government, the guard told him that Hitler was right about the Jews and "we will finish what he started".

London was as much astonished as frightened: "This was the first time in my adult life that I was insulted because I was a Jew and was held to be a criminal because of my race — and that by a man from State Security of a socialist country, a member of the Communist Party. Was it possible that the mentality of the SS had risen in our ranks?"

Western Communists of Jewish origin rushed to prove their loyalty by supporting the pogrom; not out of fear of physical violence, for no one could threaten them in the West, but out of fear of the ostracism that would follow a falling out with the Left. Maxime Rodinson, a French Communist who defended the purges, later said that he could not face "the most obvious facts" about the fascistic nature of the Communists because of his "visceral need not to renounce a commitment that has illuminated one's life, given it meaning, and for which many sacrifices have often been made".