Left-wing antisemitism got going during the foundations of the socialist movement in the late 19th century when some parts of the left, often as a tactical ploy, identified "the Jew" with finance and capitalism.
August Bebel, the German Social Democrat leader, shook his head and called this the "socialism of fools".
There was much foolishness in Britain, too. "Wherever there is trouble in Europe, wherever rumours of war circulate and men's minds are distraught with fear of change and calamity," warned the Independent Labour Party (ILP) in 1891, "you may be sure that a hooked-nosed Rothschild is at his games somewhere near the region of the disturbances."
Left-wing antisemitism never went away. It became the "anti-imperialism of idiots" in the last third of the 20th century, when vicious, well-funded and long-running anti-Zionist campaigns were conducted by the Stalinist states, in alliance with the authoritarian Arab states and parts of the western New Left.
Those campaigns laid the ground for the form taken by left-wing antisemitism today - antisemitic anti-Zionism.
Antisemitic anti-Zionism bends the meaning of Israel and Zionism out of shape until both become fit receptacles for the tropes, images and ideas of classical antisemitism. In short, that which the demonological Jew once was, demonological Israel now is: malevolent, full of blood lust, all-controlling, the obstacle to a better, purer, more spiritual world.
Antisemitic anti-Zionism has three components. First, it is a political programme aiming at the abolition of the Jewish homeland.
Second, it is a demonising intellectual discourse and system of concepts: "Zionism is racism"; Israel as a "settler-colonialist" which ethnically cleansed the "indigenous" people, went on to build an apartheid state and is now engaged in an incremental genocide against the Palestinians.
Third, it is a global social movement (the Boycott Divestment and Sanctions or BDS movement).
The concern about Jeremy Corbyn is not that he indulges in antisemitism himself. It is that he indulges the antisemitism of others unless they come wearing a uniform and speaking German. When he is faced with antisemitic anti-Zionism, he overlooks the antisemitism. For example, he defended the antisemitic Palestinian Islamist Raed Saleh, even though Saleh's vile Jew-hatred was a matter of public record (hell, a matter of court records, come to that).
Today is springtime for left-wing antisemitic anti-Zionism. We have a left-wing poet, Tom Paulin, who compares the IDF to the SS; a left-wing Church of England vicar, Stephen Sizer, who links to an article saying the Jews did 9/11, and then says, anyway, prove that they didn't; a left-wing comedian, Alexei Sayle, who jokes that Israel is the Jimmy Saville of the nations; a left-leaning peer, Jenny Tonge, who demands an enquiry into whether the rescue mission sent by Israel to Haiti had a secret agenda of harvesting organs for Jews in Israel. And so on.
The left got into this mess because it wanted to dissolve Jewish peoplehood in the solvent of progressive universalism. We thought the proletariat would make a revolution that would solve "the Jewish question" once and for all.
But when the European socialist revolution failed and fascism and Nazism triumphed, culminating in the Holocaust, the appeal of the left's universalism was in tatters.
In response to that rupture in world history - when Europe "vomited up its Jews" to quote the Israeli historian Zeev Sternhell - the Jews insisted on defining their own mode of participation in universal emancipation: ie, Zionism and the creation of the state of Israel.
Tragically, parts of the left - not all - didn't get the memo. And everything hinges on this failure of imagination.
Anti-Zionism became the reactionary programme to eradicate the Jewish homeland, a programme which converged with Arab nationalism and, latterly, even with radical Islamism, both of which could now be coded as singularly progressive by the left.
Leading academic Judith Butler said Hamas and Hezbollah are now "part of the global left". Or, put more simply by Jeremy Corbyn, they are "friends".
At that point, of course, the left is lost.
