Of the fighting faiths that flourished during the ideologically drunk 20th century, anti-Semitism has been uniquely durable. It survives by mutating, even migrating across the political spectrum from the right to the left. Although most frequently found in European semi-fascist parties, anti-Semitism is growing in the fetid Petri dish of American academia, and is staining Britain’s Labour Party.

In 2014, before Naseem “Naz” Shah became a Labour member of parliament, she shared a graphic on her Facebook page suggesting that all Israelis should be “relocated” to the United States. She seemed to endorse the idea that the “transportation cost” would be less than “three years of defense spending.” When this was recently publicized, “Red Ken” Livingstone, former Labour mayor of London, offered on the BBC what he considered a defense of her as not anti-Semitic because “a real anti-Semite doesn’t just hate the Jews in Israel.” Besides, Livingstone said, Hitler was a Zionist (for supposedly considering sending Europe’s Jews to Palestine) “before he went mad.” As mayor, Livingstone praised as a “progressive voice” an Egyptian cleric who called the Holocaust “divine punishment.”

Labour’s leader, Jeremy Corbyn, says he wants to cleanse Labour of such thinking. But Corbyn hopes to host at the House of Commons a Palestinian sheikh who calls Jews “bacteria” and “monkeys” and has been accused of repeating the “blood libel” that Jews make matzo using the blood of gentile children.

Leftist anti-Semites invariably say they hate not Jews but Zionism, and hence not a people but a nation. Israel was, however, created as a haven for an endangered people. Jonathan Sacks, former chief rabbi of the United Hebrew Congregations of the Commonwealth, refutes the canard that “hating Israel is not the same as hating Jews” by saying:

Criticism of Israel is not necessarily anti-Semitic or anti-Zionist. When Sacks asks his audiences if Britain’s government can be criticized, everyone says yes. But when they are asked, “Do you believe Britain should not exist?,” no one says yes. Then Sacks tells his audiences: “Now you know the difference.”

“It is very easy to hate,” says Sacks. “It is very difficult to justify hate.” Anti-Semitism’s permutations adapt it to changing needs for justification. In the Middle Ages, he says, Jews were hated for their religion. In the 19th and 20th centuries, they were hated for their race. Now they are hated for their nation. “The new anti-Semitism can always say it is not the old anti-Semitism.”

But it is. It remains, Sacks says, “essentially eliminationist.” It disguises its genocidal viciousness, insisting that it seeks the destruction not of a people but only of the state formed as a haven for this people that has had a uniquely hazardous history. The international “Boycott, Divestment and Sanctions” movement, supported by many American academics, aims not just to pressure Israel to change policies, as South Africa was pressured to abandon apartheid, but rather to de-legitimize Israel’s existence as a nation.

Sacks says that when bad things happen to a healthy society, it asks: What did we do wrong? A fraying, insecure society asks: Who did this to us? Sacks notes that although Jews were never more than 2 percent of Germany’s population, this did not protect them from becoming the explanation for Germany’s discontents.

In a conversation with a supposedly “moderate” British Muslim leader, Sacks asked, “Does Israel have a right to exist within any borders whatever?” The leader replied: “Your own prophets said that because of your sins you have forfeited your right to your land.” To which Sacks responded mildly: “But that was 2,700 years ago and surely the Jews have served their sentence.”

After World War II, Western nations strove to develop what Sacks calls “a cultural immune system” against anti-Semitism with Holocaust education and other measures. The immune system is not weakening in Britain, other than among Muslim immigrants and leftists eager to meld their radicalism with radical Islam.

Labour’s leader before Corbyn, Edward Miliband, who led the party in the 2015 general election, is Jewish, as was the Conservative Party’s greatest 19th-century leader (Benjamin Disraeli). Former Conservative Prime Minister Harold Macmillan, who was educated at Eton, noted, perhaps regretfully, certainly indelicately, that Margaret Thatcher’s Cabinet included more “old Estonians than old Etonians.” This was not anti-Semitism, just a jest too fine to forgo.

Seven decades after the Holocaust, some European nations have, remarkably, anti-Semitism without Jews and Christian anti-Semitism without Christianity. Britain just has a few leftists eager to mend their threadbare socialism with something borrowed from National Socialism.

© 2016, Washington Post Writers Group