JEREMY CORBYN has spent a remarkable proportion of his life on “demos”—indeed, it is no exaggeration to say that protesting is his core competence. This week, however, the Labour leader found himself on the receiving end of a demonstration. Two Jewish groups, the Board of Deputies of British Jews and the Jewish Leadership Council, organised a protest in Parliament Square to draw attention to Mr Corbyn’s anti-Semitism problem.

The demonstration was only about a thousand strong. The organisers forgot to bring a PA system so it was impossible to hear what was being said. Only a handful of people joined in with the chant of “Mural, mural on the wall, who is the biggest racist of them all—Corbyn!” But this was nevertheless a significant moment: a group of Jews standing outside Parliament, protesting about the prevalence of anti-Semitism not on the fascist extreme but at the heart of one of Britain’s two biggest parties.

The immediate cause of the protest was a recently unearthed comment that Mr Corbyn posted online in 2012 in response to a piece of London street art. The mural in question is a blatantly anti-Semitic portrait of a group of capitalists, most of them with hook-noses, playing Monopoly on a table resting on the backs of naked workers. The local authority ordered the mural be painted over. Mr Corbyn leapt to the artist’s defence, writing on his Facebook page: “Why? You are in good company. Rockerfeller [sic] destroyed Diego Viera’s [Rivera’s] mural because it includes a picture of Lenin.” The discovery of the post proved too much for many leading British Jews, who have written to Mr Corbyn with three complaints: that the Labour Party contains pockets of anti-Semitism; that Mr Corbyn has repeatedly turned a blind eye to such noxious attitudes; and that previous attempts to deal with it have proved inadequate.

They are right on all three counts. Jewish Labour MPs such as Luciana Berger have been subjected to anti-Semitic rants and intimidation from supporters of the hard left. Jewish students have abandoned Labour groups because they feel threatened and vilified. One source of the anti-Semitic infection is the hard left, which is almost defined by its hostility to Israel and capitalism. There is nothing necessarily anti-Semitic about either position. But in the heat of political debate, distinctions can blur and ancient hatreds flame. Hard-leftists habitually refer to Jews as “Zios”. The artist behind the London mural said it was not an attack on Jews but on capitalists such as Rockefeller and Warburg.

Another source of Labour’s anti-Semitism is British Muslims. A poll last September found that 55% of Muslims held anti-Semitic attitudes, with 27% believing that “Jews get rich at the expense of others”, compared with 12% of the general population. Mehdi Hasan, a Muslim writer, says that “weird and wacky anti-Semitic conspiracy theories are the default explanation for a range of national and international events.” For all their disagreements on issues like gay rights, hard-leftists and Muslims forged a lasting alliance in the Stop the War movement against the invasion of Iraq.

Mr Corbyn has done more than turn a blind eye to anti-Semitism. He has had tea in Parliament with Islamist radicals such as Sheikh Raed Salah, who has claimed that “a suitable way was found to warn the 4,000 Jews who work[ed] every day in the Twin Towers” to stay at home on September 11th 2001. He has appeared on Iranian national television, despite the fact that the regime issues wild threats to destroy Israel. One of his old friends, Ken Livingstone, has repeatedly asserted that Hitler supported Zionism in the early 1930s.

This week’s row was proof in itself that previous attempts to tackle the problem have failed. Several Labour MPs joined the protests in a public rebuke to the party leadership. But is there also a chance that it marks a turning-point? Mr Corbyn has issued a statement recognising that “anti-Semitism has surfaced within the Labour Party”, apologised for his misjudgment over the mural and offered to meet Jewish leaders. His aides are reportedly “rattled” by the fallout from the row, which represents more of a threat to his reputation for sanctity than his links to IRA activists.

Speak no evil

But there are powerful reasons for believing that the problem will not be tackled. One is biographical. Mr Corbyn has spent his life moving in far-left circles since arriving in London in the early 1970s. His instinct is that there are no enemies to the left—that fellow protesters in the Socialist Workers Party or International Marxist Group should be forgiven their peccadillos (such as believing in armed revolution) because they believe in social justice. Mr Corbyn’s supporters have the same attitude. This week they rallied to his defence, claiming that the establishment was conjuring up the anti-Semitism row to discredit their champion.

Another reason is strategic. British Jews—particularly those who support Israel—are being marginalised in the Labour Party. There are 3m Muslims in Britain compared with about 284,000 Jews, and they are concentrated in areas vital for Labour’s future, such as Birmingham and Manchester. The philo-Semitic tradition in the Labour Party, exemplified by Harold Wilson and James Callaghan, is dying.

The most important reason is philosophical. Mr Corbyn has devoted much of his life to protesting against racism. But for him, racism is linked to class and exploitation. It is about privileged people doing down the marginalised, and saintly activists like Mr Corbyn riding to their rescue. But the Jews are perhaps the world’s most successful ethnic minority. They have almost always succeeded by the sweat of their brow rather than the largesse of activists or government programmes. They are often hated precisely because they have succeeded where other marginalised groups have failed. The danger is not that Mr Corbyn will continue to ignore anti-Semitism after this week’s protests. It’s that he doesn’t understand what anti-Semitism is.