This story is less to do with individual wickedness than with what has happened to the Left. The stuff that Mr Livingstone garbled about Hitler supporting Zionism comes from a book by Lenni Brenner called Zionism in the Age of the Dictators. Brenner, a Trotskyite who renounced his own Jewish upbringing, sought to prove that Zionism in the Thirties was a Jewish collaboration with Hitler. In the early Eighties, when the book was published, Mr Livingstone was in charge of Labour Herald, the newspaper vehicle for his hard-Left takeover of London Labour (printed with the help of money from Colonel Gaddafi’s Libya). Labour Herald gave Brenner’s book an ecstatic review. It was part of a growing trend.

During the Sixties, much of the Left moved from its traditional concern with the organised working class to a greater focus on “the wretched of the earth”. The phrase was the title of a book by the Marxist philosopher, Franz Fanon, who heavily influenced, among others, the young Barack Obama. In this picture, the greatest enemy was colonialism, and the perpetual victim was the Third World, or what is nowadays called the Global South. Violent struggle by the victims to cast off their shackles was advocated.

In the same period, the Soviet Union, which had frequently used anti-Semitic propaganda to reinforce its internal repressions, began to export the stuff. In the Middle East, where it sought advantage against the United States and the West, such tropes were particularly effective. Many in the Muslim world craved support for the idea that Israel, which had so amazingly trounced its Arab neighbours when they attacked it in 1967, was part of a global plot by Western power and money to keep them in subjection.