So, we’re back to the “Jewish Question”? The current antisemitism crisis on the left has not come out of nowhere. Instead, it has its roots in a tradition on the left itself, which, at best, has always had difficulty in responding swiftly to antisemitism and, at worst, excused or condoned, even promoted it. It is not, of course, the only tradition on the left, but unless we understand this history, we won’t get very far in resolving today’s crisis.

We need, above all, to think about why some on the left have always seen Jews as a problem and why they have helped the idea of a “Jewish Question” to re-emerge with such potency. At root is the thought that if antisemitism exists, it must have something to do with how Jews supposedly behave. That supposed behaviour may be described in different ways – sometimes it has an economic character, sometimes a social one, sometimes a political one. But what is common is the idea that Jews are to blame for antisemitism and that to protest against them is understandable, or even necessary.

This first became a serious problem on the left in the late 19th century, as antisemitism first became a political force in the modern world. Some on the left flirted with the response that there might be something progressive about antisemitism: that it was a kind of anti-capitalism, however crude, which could be harnessed to the socialist cause. They also thought that philosemitism was more of a problem, because it supposedly encouraged Jews to make too much of (or even fabricate) antisemitism and to resist assimilation. One criticism of this approach at the time was to call it the “socialism of fools”, a problematic formulation because it suggested that antisemitism was still some kind of socialism.

As antisemitism was radicalised by the Nazis – it no longer being enough to exclude Jews when they should be wiped off the face of the Earth – this way of thinking made it difficult for too many on the left to prioritise solidarity with Jews. Neither the Social Democrats nor the Communists in Germany made opposition to antisemitism a major issue, nor did the Resistance across Europe. The fear was that to highlight the fight against antisemitism would alienate potential supporters. This is not to ignore some wonderful examples of solidarity, though the repeated invocations of Cable Street can give a misleading picture. The Communist party soon switched to loyally supporting the Hitler-Stalin pact, which effectively delivered large numbers of Jews up to the Nazis.

‘The repeated invocations of Cable Street [the 1936 anti-facist demonstration in London] can give a misleading picture.’ Photograph: David Savill/Getty Images

When the Soviet Union was finally forced to fight the Nazis, the suffering of Jews was deliberately and repeatedly downplayed. But after the war, things got much worse. The Soviet Union not only suppressed knowledge of what had been done to Jews but launched its own vicious antisemitic project, one that would have culminated in another genocide had Stalin not died.

This campaign matters because it was around this time that some key elements of today’s antisemitism on the left were first formulated. The charge laid against Jews then was that they were cosmopolitans and Zionists. This may seem like a bizarre contradiction: how can one, after all, be both a cosmopolitan and a Zionist? But what connected them is the idea that Jews are a problem, that as cosmopolitans they are more loyal to each other across national borders and, as Zionists, are loyal to another, foreign state. The charge of cosmopolitanism is heard less frequently these days, though one finds echoes of it in the idea that Jews are responsible for the evils of globalisation. The charge of Zionism, though, has now become absolutely central to today’s version of the “Jewish Question”. What began as a Stalinist cry was taken up in some on the New Left, which helped shape the world view of Jeremy Corbyn and many of his supporters.

For both Stalinists and that part of the New Left, Zionism is a racist ideology that pits the interests of Jews against the interests of everyone else. Furthermore, the state of Israel is an integral part of the western imperialist power structure that exploits and oppresses the rest of the world and the Palestinians in particular, whose land Jews have plundered and colonised and whom they keep in a state of permanent subjugation.

The Soviet Union formulated its approach within the context of the cold war, when it often appeared to support anti-colonial, national liberation struggles, although only for strategic reasons. Those on the left who (rightly if often too uncritically) supported those struggles, especially in Vietnam, where the Americans were so clearly the enemy, slipped fatally, however, into embracing this anti-Zionism into their world view, even though the Israel-Palestine conflict had such clearly different roots.

At the same time, they found it unbearable to acknowledge what was glaringly obvious – that the establishment of the state of Israel was profoundly connected to the Holocaust, which had changed everything for Jews. To integrate anti-Zionism into an anti-imperialist, anti-western, anti-American world view therefore also meant either denying or (better) reinterpreting the Holocaust. Holocaust denial is not an accidental feature of today’s antisemitism, but it is more common to downplay what happened to Jews as Jews. So the Holocaust has to be thought about only in universal terms, as only one genocide among many and one that supposedly excludes the others. (Actually, of course, it is the other way around: thinking about the Holocaust helps people think about other genocides.) Indeed, some have gone further. Not content with accusing Israel of being like apartheid South Africa, it is supposedly guilty of genocide itself… against the Palestinians.

If such purported behaviour makes people antisemitic, it is understandable and part of a fundamentally progressive view of the world, which can be harnessed to the cause. We are back then to where we started, with Jews as the problem, only with this difference: what was previously attributed to Jews inside nation states is now attributed to the Jewish state on the international stage.

There has always been, though, another tradition on the left, which has never accepted the very idea of a “Jewish Question”. What it understands is that there is a question of antisemitism; that Jews are not responsible for antisemitism but antisemites are; that Jews are not a problem but antisemites are. Antisemitism is not something that should be excused or condoned. It has to be fought wherever it shows its face, even – and sadly now more than ever – when that face is on the left.

• Philip Spencer is emeritus professor of Holocaust and genocide studies at Kingston University and a visiting professor in politics at Birkbeck College. He is the co-author with Robert Fine of Anti-Semitism and the Left: On the return of the Jewish Question, Manchester University Press, 2017