I’m trying to imagine the left’s reaction if it emerged that a leading politician had once lavished praise on a century-old book that not only trotted out racist stereotypes about, say, black people and their supposed characteristics, but whose central thesis rested on an ancient, hostile assumption about that group. Would good, progressive folk be rushing to defend that politician by saying the author of the book in question had also written lots of important, non-offensive things, and that other people had quoted that author too, so this was a fuss about nothing – or would they be appalled and even sickened that a contemporary politician could praise such a text without so much as mentioning the racism within it?

It turns out that the answer is: it depends which side the politician is on, and also perhaps which ethnic minority is involved. If the politician is the current leader of the Labour party and the minority involved are Jews, well, then it seems the usual progressive reflexes don’t always kick in.

No one is arguing Corbyn had to denounce the whole book. He could simply have nodded to the problem with a tiny caveat

In today’s Times, the columnist Daniel Finkelstein has dug out a 2011 reissue of JA Hobson’s 1902 work, Imperialism: A Study. The foreword was written by Jeremy Corbyn in 2011. Across eight pages, the then Labour backbencher lavishes praise on the book. His very first sentence describes it as a “great tome”. Among other things, he calls it “very powerful,” “brilliant”, as well as “correct and prescient”. The trouble is, Hobson was not just an accomplished analyst of international politics – for the Manchester Guardian, as it happens – but an egregious anti-Jewish racist.

In a previous book, that bigotry was expressed in the most florid terms. Hobson wrote that the war between Britain and the Boers in South Africa was the work of “a small group of international financiers, chiefly German in origin and Jewish in race,” going on to say that the stock exchange, the press and even the liquor trade was “in the hands of Jews”. He was articulating what was already a familiar antisemitic trope: that the Jews secretly pull the levers of world events, and that they deliberately draw otherwise peaceful nations into war.

That claim is also present in Imperialism, the book Corbyn introduced so warmly. There, Hobson writes that “men of a single and peculiar race, who have behind them many centuries of financial experience … are in a unique position to control the policy of nations”. When he speaks of a “single and peculiar race”, it’s clear he’s talking about Jews. In that same paragraph, Hobson plucks on an anti-Jewish string that still resonates today. He asks if any European state would dare contemplate a great war, “if the house of Rothschild and its connections set their face against it?”

Now, plenty of people have spoken in general about Hobson – who was indeed an important and influential thinker on the British liberal left – without feeling the need to note Hobson’s bigoted views of Jews, which were hardly uncommon in that period. Fair enough. But Corbyn was not merely referring to Hobson and his thought in general: he was writing an extended assessment of a specific text – engaging directly with it. And yet across the eight pages Corbyn wrote, there is not so much as an acknowledgment of the racism within that text.

On the contrary, the bit Corbyn praised as “correct and prescient” was, in his words, “Hobson’s railing against the commercial interests that fuel the role of the popular press,” which appears squarely in the section where Hobson’s target is “this little group of financial kings”, these “cosmopolitan” men who he had already identified as Jews. (The chapter, incidentally, is called “Economic Parasites of Imperialism,” with “parasites” an image recurrent in anti-Jewish propaganda.) This is not a mere aside by Hobson that might accidentally be overlooked in a skim-read by a busy politician. There are pages and pages of it.

No one is arguing that Corbyn was obliged to denounce the whole book. He could simply have nodded to the problem with a tiny caveat: something like, “Despite some passages that read uncomfortably to the modern ear …” But there is nothing like that. He might have made the move Finkelstein himself made when writing recently about Churchill, in a column headlined: “Winston Churchill was a racist but still a great man”. Corbyn could have said something similar about Hobson or his book. But he didn’t do that either. A Labour spokesman has said that: “Jeremy completely rejects the antisemitic elements of [Hobson’s] analysis.” But if that’s true, why did he not say so when he wrote about it?

Perhaps the Labour leader’s explanation will be the same one he offered for his defence of a mural depicting hook-nosed, Jewish bankers playing Monopoly on the backs of the poor: that he simply did not see the racism. But in the Hobson text, it’s there in black and white. It would be very hard to miss, especially if you’re a “lifelong anti-racist” as Corbyn always insists he is. But perhaps that will be what he’ll say: that he couldn’t see the racism even when it stared him in the face. Because the only other explanation available is that he didn’t object to this part of Hobson’s analysis – as he did to other parts, describing one element of the book as “strange” – because he didn’t see anything wrong with it.

We all know that it’s painful to admit flaws in those we admire. Corbyn should have done it about Hobson, but did not. Now that task falls to Labour MPs, members, supporters and voters. The Labour leader may tell himself that he is the victim here, a serially unlucky anti-racist who means well, but keeps overlooking racism against Jews even when it’s right in front of him, whether on the platforms he shares or the books he praises. Now the rest of the Labour family have to decide how much longer they are willing to indulge that delusion.

• Jonathan Freedland is a Guardian columnist

• This article was amended on 2 May 2019 to omit a superfluous reference to another minority.