When is a Jew not a Jew? When it’s a British Zionist who doesn’t get irony, apparently.

Another week, another case of Labour leader Jeremy Corbyn’s alleged anti-Semitism, followed by the inevitable nano-nuancing and micro-analysis to establish whether this was a smoking gun or just a ballistic weapon coming into contact with a wholly unrelated cloud of steam.

One of the difficulties throughout the saga of Labour anti-Semitism is that much of the radical left—here defined as Bennites leftwards—do not accept anyone’s right to put them on trial for racism.

As far as they are concerned, they are the ones who have always fought racism while others, at best, turned the other cheek. They took the blows. They endured the arrests. They sacrificed their careers in order to stand up to racism for decades. Who are these Blairite bombers and Tory Tebbit-testers to now roll up and accuse them of racism?

Thus for older Corbynites in particular—versed less in the modern language of intersectionality and more in old images of Corbyn fighting against apartheid—none of this has any legitimacy: not the accusers or the accusation, nor the trial, the judge, or the jury.

That Corbyn should even be mentioned in the same breath as racism, other than to describe his opposition to it, is preposterous. Whatever explanation is dug up to defend the Labour leader, they will accept it.

For them, the main legacy of 2018 may be a lasting suspicion of Jewish opinion and influence in politics and media—a process that will likely increase anti-semitism on the radical left like never before.

That word “suspicion” is key. Corbyn has never been accused of the most blatant anti-Semitic tropes, the racist nature of which virtually everyone agrees on: the blood libel, Holocaust denial and the such like. Until this summer, the main charge against him was a tolerance of anti-Semitism in others, rather than his own views.

But a key driver of the row within Labour has been the lack of an agreed definition of what anti-Semitism actually is—with the IHRA definition of anti-Semitism, which is supported by most mainstream Jewish groups, proving a major flashpoint.

The IHRA row does not shed light on what is happening on the radical left, however. It provides a list of various manifestations of anti-Semitism, some of which are contested by Palestine activists. It does not tell us where those manifestations come from.

Among some on the radical left, there is a suspicion of Jews that is centred on Israel and Palestine.

Identifying this suspicion is critical to realising both the alleged anti-Semitism of some Corbynites, and why others cannot see it. It is not borne of money-lending or the death of Christ. It is based on views of Israel.

If a Jewish person engages in politics or politically sensitive fields of public life, particularly in a way that is inimical to the radical left, there is a type of radical left-winger who will want to know: “are they Zionists?” If they are, that is then used as the explanation for other political views. This is how suspicion manifests.

Crucially, it does not lead to negative views of all Jews. Rather, it sorts Jews into Good Jews and Bad Jews. The Bad Jews support Israel. The Good Jews oppose it. Therefore, some Jewish people end up praised and supported, while the majority of Jews in British politics are discredited as “Zionists,” regardless of the specifics of their beliefs.

Because it does not condemn all Jews, and because it judges them on their choice of worldview, those who engage in this kind of thinking do not see it as racist. The fact that Jewish identity is closely tied to Israel does not, by this thinking, make it unbreakably so—and those who do not break with Israel can be blamed for what is seen as a political choice like any other.

Is this anti-Semitism? Palestine activism in the UK is replete with talk of Zionist lobbies (which doubtless exist as they do for other states but are hardly all-powerful) and pro-Israeli control of politics and the media. Dialogue with Israelis is rejected if it is seen to legitimise Israel’s existence. Either way, the effect is that Jewish people are regarded through a lens that others would not be.

It does not have to be this way—nor does it seem remotely productive—but it is the product of treating the outright repudiation of Zionism as a concept, and those who support it (a majority of British Jews), as a prerequisite for true solidarity with Palestinians. And it is little surprise if those who for decades have existed in this atmosphere do not see it as untoward.

A useful thought experiment for the radical left is this. Is it racist to share a platform with Tommy Robinson in supposed defence of child sex abuse victims? Is it racist to demand Muslims apologise for Islamic fundamentalist terrorism? Is it racist to claim that Islamophobic incidents are faked or staged? And is it all ok if someone quotes Ayaan Hirsi Ali while doing so?

As for Corbyn himself, what is there to say? He does not engage in the most blatant anti-Semitism, and so each individual incident can be acrobatically explained away. But put them all together, and a lot of apparent things must be false, and a lot of unlikely things must be true, for us to say with certainty that Corbyn does not see the world through this discriminatory lens, too.