Many in the British Labour Party will not look back on the past week fondly. A party that has spent decades advancing the cause of racial equality now finds itself at the center of the recrudescence of antisemitism in public life.

The crisis began after a Labour MP, Naz Shah, shared antisemitic Facebook posts comparing Israel and the Nazis and recommending the “transportation” of Israelis to the USA. Shah was suspended from the party and quickly admitted her wrongdoing. Despite this, the former MP and mayor of London, Ken Livingstone, defended her. He insisted that Shah was “the victim of a well orchestrated campaign by the Israel lobby,” claimed, wrongly, that Hitler supported Zionism “before he went mad and ended up killing six million Jews,” and stated, “A real anti-Semite doesn’t just hate the Jews in Israel.” Unsurprisingly, Livingstone too was suspended.

The controversy is not a one-week phenomenon. Its antecedents reveal the changing nature of anti-Jewish prejudice in Britain.

Over the past decade, perspectives on Israel have changed in the Labour Party. The Israeli-Palestinian conflict is partly to blame. Under Ed Miliband and Jeremy Corbyn, Labour gradually abandoned the positions of Tony Blair. Whereas Blair strongly supported the Israeli war against Hezbollah in 2006, Miliband condemned the “unacceptable and unjustifiable” targeting of civilians by Israel during the 2014 Gaza conflict. Corbyn supports a boycott of agricultural produce from West Bank settlements and the severing of links to Israeli universities that conduct research for the IDF. Several trade unions, including Unite, Unison, and the GMB, amongst the largest donors to Labour, have adopted Boycott, Divestment, and Sanctions (BDS) as official policy. Jewish support for the Labour Party has declined. Before the 2015 general election, only 22% of voters expressed a preference Labour.

But something more malign is afoot. Earlier this year, readers of the Jewish Chronicle found the headline “Labour’s Shame” blaring from the doorstep. The newspaper drew attention to language on the far-left fringes of the party that attempted to delegitimize Israel and its supporters by equating Zionism and Nazism, denouncing opponents of BDS as racists, and proclaiming antisemitic conspiracy theories. A dismal procession of minor party officials have been expelled for praising Hitler, demanding the destruction of Israel, or hurling antisemitic abuse at supporters of Israel. Jewish students in Labour Party clubs on university campuses report frequent use of pejoratives, the stifling of debates opposing BDS, and the dismissal of complaints about racial abuse.

The nature of antisemitism has changed. The Aliens Act(1905), preventing Jews fleeing the Russian pogroms from seeking sanctuary in Britain, and the decision of 1930s governments to limit entry to refugees from Nazi Germany, reflected fears of difference. But subsequently, assimilation, intermarriage, and falling Christian observance led Jews to be seen as part of, rather than apart from, the nation. David Cesarani points out that in Britain, and much of Europe, “Jews are not isolated, as they were in the 1930s and 1940s, but find themselves enjoying unprecedented solidarity.”

Nevertheless, Anthony Julius shows that while cultural, social, economic, and religious prejudices have waned, they still exist, often alongside a pernicious anti-Zionism. Let’s be clear: there is nothing anti-Jewish in criticizing the actions of the IDF, settlement building, the occupation of the West Bank, or the discrimination shown towards Arab minorities in Israel. But suggestions that supporters of Israel suffer from a moral deficiency, that the existence of Israel is illegitimate, that Israel, alone of all countries should be subject to special punishment for its transgressions, or that an organized conspiracy impels Israeli interests, carry ominous intonations of the past.

Demographic change helps explain the growing acceptance of Jews. Until the late 1950s, Jews were the largest minority in Britain. Thereafter, immigration from the West Indies, India, Pakistan, and former colonies in Africa, transformed Britain into a racially diverse and multicultural society. But at a moment in which ideas of Britishness were in flux, conceptions of whiteness expanded to include Jews.

Labour identifies as an avowedly anti-racist party. Labour governments passed the Race Relations Acts (1965, 1976, 2000) and established a Commission for Racial Equality. In the 1990s and 2000s, the administrations of Tony Blair began attempts to dismantle institutionalized forms of racism endemic to public life, and pushed for the humane treatment of immigrants and refugees despite media and internal party opposition.

The Labour Party is not antisemitic. Most members, officials, and MPs are horrified about the controversy. But the fact that I need to explain this suggests a problem exists.

Complacency is one concern. The commitment to fighting racism is not matched by vigilance over antisemitism. Corbyn has fought for Palestinian rights for decades. But he has done so carelessly, speaking at and funding events for a group led by a Holocaust denier, and describing representatives of Hamas and Hezbollah as “friends.” The MP Diane Abbott, and Unite leader Len McCluskey, both allies of Corbyn, described the latest controversy as a “smear” and as “mood music.” Corbyn initially told the BBC “there’s no crisis.” More broadly, some members distinguish antisemitism from anti-Zionism, or deny that anti-Jewish prejudice is equal to other forms of racism.

Unexamined is what the crisis looks like to British Jews. Despite unease over Israeli policies, 93 percent say that Israel forms part of their identity. Recent events do more than give offense. They belittle a core sense of being for many of Britain’s 280,000 Jews.

The antisemitism crisis belongs to Labour’s far-left flank. These are the margins where Corbyn toiled for decades as a backbencher and, as an unpopular leader with MPs, has brought into the party mainstream. Corbyn has recruited thousands of new members, but senior figures worry they include hard-left factions hostile to Israel, hitherto prevented from joining the party. An independent inquiry into antisemitism has been announced, but MPs feel Corbyn cannot manage the crisis.

There is no suggestion that Jeremy Corbyn is an antisemite, but there is a suspicion that some of his friends are.