By Patrick Kingsley

Swastikas daubed on a Jewish cemetery in France. An antisemitic political campaign by Hungary’s far-right government. Labour lawmakers in Britain quitting their party and citing ingrained antisemitism. A Belgian carnival float caricaturing Orthodox Jews sitting on bags of money.

And that was just the past few months.

The accumulated incidents in Europe and the United States have highlighted how an ancient prejudice is surging in the 21st century in both familiar and mutant ways, fusing ideologies that otherwise would have little overlap.

The spike is taking place in a context of rising global economic uncertainty, an emphasis on race and national identity, and a deepening polarization between the political left and right in Europe and the United States over the conflict between Israel and the Palestinians.

“There’s an ideological pattern that is common,” said Günther Jikeli, an expert on European antisemitism at Indiana University. “The world is seen as in a bad shape, and what hinders it becoming a better place are the Jews.”

Antisemitism has become a section of today’s political Venn diagram where the far right can intersect with parts of the far left, Europe’s radical Islamist fringe, and even politicians from America’s two main parties.

That confluence is new, experts say, as is the emergence of an Israeli government that has sidled up to far-right allies who praise Israel even as they peddle antisemitic prejudice at home.

“It creates a landscape that is very confusing and where things are more blurry than in the past,” said Samuel Ghiles-Meilhac, an expert on Jewish history at the Institut d’Histoire du Temps Présent, a government-funded research group in France.

Polling suggests that antisemitic attitudes may be no more widespread than in the past, particularly in Western Europe, where Holocaust remembrance has become a ritual for most governments.

Despite this, bigots have seemingly become more brazen, creating a climate that has made antisemitism far more permissible and dangerous.

In recent decades, Western antisemitism has tended to trace the contours of the Israeli-Palestinian conflict, spiking and ebbing in correlation with spasms of violence between the two sides. But since the 2014 war in Gaza, researchers say, antisemitic incidents have remained at high levels.

“And that’s kind of worrying because it means it has become normal to act in antisemitic ways,” Mr. Jikeli said.

Those include acts of violence. In 2018, France reported a 74 percent spike over the previous year in antisemitic incidents, with more than 500 attacks including the murder of a Holocaust survivor in her own home. President Emmanuel Macron called it the worst level of antisemitism since World War II.

In Germany over the same period, violent antisemitic attacks — 62 of them — rose by 60 percent, while all antisemitic crimes rose almost 10 percent to 1,646, according to government statistics.

Around Europe, where the popularity of the far right has been boosted by economic uncertainty and fears over migration, almost 90 percent of Jews believe that antisemitism has increased in their country in the last five years, according to surveys by the European Union.

For decades after World War II and the Holocaust, antisemitism was mostly consigned to the political fringes, which is no longer the case. It is now more

“Today, mainstream European and North American politicians, even presidents, premiers and prime ministers, don’t hesitate to flirt with or embrace overtly antisemitic messages and memes,” said David Nirenberg, dean of the Divinity School at the University of Chicago and an expert on Jewish history.

“This electoral utility of antisemitism feels new to me, newly flexible, and therefore newly dangerous,” Mr. Nirenberg added.

Far-right parties often portray Jews as a cosmopolitan threat to national identity, especially in regions where the stereotype has been used historically. In Hungary, Prime Minister Viktor Orban has been able to present the Jewish billionaire George Soros as a secret instigator of Muslim immigration.

In Poland last month, a far-right newspaper sold inside the Parliament ran a front-page headline saying “How to spot a Jew,” alongside a condemnation of a historian who researches Polish complicity in the Holocaust.

On the far left, some politicians have associated Jews with the failings of capitalism and conspiracies about supposed control over the global economy. Those complaints are now heard on the fringes of the Yellow Vest movement in France.

President Trump himself embodies the contradictions of the moment. Mr. Trump has openly courted white nationalists, saying they include “some very fine people,” even as they marched in the style of the Ku Klux Klan, gave stiff-armed Nazi salutes and chanted slogans like “Jews will not replace us.”

During his campaign, he attacked Hillary Clinton with a Twitter post that included her image, a Jewish star, and a pile of money.

At the same time, the president has boasted close relations with Prime Minister Benjamin Netanyahu and offered full-throated support to Israel, including moving the United States Embassy to Jerusalem, even absent progress toward a settlement with the Palestinians.

That more strident support has now been greeted with more strident opposition, most obviously from Representative Ilhan Omar of Minnesota, one of the first two Muslim women elected to Congress.

She has been widely condemned for peddling antisemitic stereotypes — for which she publicly apologized. Ms. Omar also was criticized for what she called undue influence of Jewish lobbies, and for what was widely interpreted as questioning American Jews’ allegiance to the United States.

The use of similar tropes by members of the Labour Party in Britain has prompted several Labour lawmakers to resign in protest. They are also common talking points in extremist Islamist circles.

“When French Muslims attack Jews in Paris or Marseille,” said Mr. Nirenberg, of the University of Chicago, “it is because Islamist discourse has taught them to understand not only the situation of Palestinians, but also the global status of Islam and even their own poverty and marginalization in France, as in some way caused by Zionists and Jews.”

But data, particularly from Germany, suggests that most contemporary antisemitism is nevertheless primarily still perpetrated by the white, far right, who are often also virulently anti-Muslim.

“It cheapens the very right struggle against antisemitism for Islamophobic bigots to weaponize it in their campaigns,” said H.A. Hellyer, a nonresident expert on Islam and the Middle East at the Atlantic Council, a research group.

“One needn’t agree with Congresswoman Ilhan Omar to recognize that she is being targeted primarily as a black, Muslim, hijab-wearing woman, and by many people whose records on combating bigotry and discrimination, or calling it out in their own ranks, are abysmal,” Dr. Hellyer added.

It is unsurprising to find a resurgence of antisemitism at a time of prolonged political and economic instability, historians and analysts say, when citizens from many different political and cultural traditions are grasping for easy explanations for sudden and complex injustices.

Just as Jews were a ready-made scapegoat during previous eras of anxiety about the pace of social change or global economic trauma, so are they again today, said Stefanie Schüler-Springorum, the head of the Center for antisemitism Research in Berlin.

“Globalization and especially the crisis of 2008 have strengthened a feeling of being at the mercy of mechanisms that we do not understand, let alone control,” Ms. Schüler-Springorum said. “From there it is only a small step to classical conspiracy theories, which have always formed the core of antisemitism.”

That step is even smaller in the social media age. Rumor and conspiracy theories have always played a role in stoking antisemitism. Today, the speed at which lies can spread, because of the internet, is without precedent.

The increasingly hard-right Israeli government led by Mr. Netanyahu is a point of divergence for the different strands of contemporary antisemitism.

Far-right political figures like Mr. Orban have drawn close to Israel, while leftist antisemites revile it. But both do so for the same reason: They perceive Israel as a country that has done its best to preserve its ethnic and religious character at the expense of a Muslim minority.

The main difference is that Mr. Orban, the prime minister of another small country fighting to preserve its ethnic identity, sees this as a virtue, whereas leftist critics of Israel, such as the supporters of the British Labour leader, Jeremy Corbyn, largely do not.

Both left and right “have the same image of Israel,” said David Hirsh, a sociologist at Goldsmiths College, University of London, and a critic of Mr. Corbyn who campaigns against the academic boycott of Israel.

“Corbyn says that Israel is a uniquely belligerent human-rights-abusing state that defends its purity at all costs against Muslims,” he said. “And I suspect that people on the far right have exactly the same picture of Israel — that it is a belligerent country that defends itself against Muslims.”

For critics of Mr. Netanyahu, this also explains why the leader of the world’s only Jewish state might find common cause with a far-right leader like Mr. Orban, despite the latter’s antisemitic leanings.

Mr. Netanyahu and Mr. Orban share an approach to domestic politics: an antipathy for liberal voices, a discomfort with Muslim minorities and a willingness to work with the far-right.

Like Mr. Orban in Hungary, Mr. Netanyahu has introduced legislation that targets civil society organizations that receive significant funding from overseas. His government has forbidden non-Jews to exercise the right to self-determination, and removed Arabic as an official Israeli language.

Recently, Mr. Netanyahu engineered an electoral pact with a racist party from the far-right fringe who could help him retain power in a general election later this year.

“I don’t believe that Netanyahu really wants a State of Israel with no Arabs, but I believe he does want a State of Israel where the position of Jews is so dominant and secure that it would never have to consider having to be a Western-style liberal democracy without an ethno-religious character,” said Derek Penslar, a professor of Jewish history at Harvard University.

“There is an aspiration for ethnocracy,” added Mr. Penslar. “It doesn’t mean there are no other ethnic groups — but only one group truly rules.”

And though the relationship between Mr. Netanyahu and Mr. Orban may trouble some in the Jewish diaspora, it may not be so troubling for Israelis themselves, said Yossi Shain, a professor of political science at Tel Aviv University.

Mr. Orban supports Israel’s right to exist, whereas his critics are perceived by some Israelis “to demean Israel’s nationalism and right to exist,” said Mr. Shain, the author of a forthcoming book addressing the subject.

“And for Israelis, that is the core of antisemitism in the modern era.”

Correction: April 4, 2019

An earlier version of this article referred incorrectly to the November 2018 election of Representative Ilhan Omar of Minnesota. She is one of the first two Muslim women elected to Congress, not the first. (Representative Rashida Tlaib of Michigan is the other.)

Correction: April 4, 2019

An earlier version of this article referred incompletely to the reaction following remarks by Representative Ilhan Omar that included antisemitic stereotypes. After she was widely condemned, she publicly apologized.