Anti-Semitism is back in Europe. Cries of “dirty Jew” during Yellow Jackets protests in France, anti-Semitic posters condemning Hungarian-American philanthropist George Soros in Hungary, a row over anti-Semitic remarks that threatens to tear the Labour Party apart in the U.K. — these are all part of the same worrying trend.

This particularly European pathology never truly went away, of course, but it had been confined, after the Holocaust, to the far-right fringes of society. Now the numbers of high-profile incidents and violent attacks are multiplying. Not only is this disease back; it is being weaponized by nationalist governments and parties on both sides of the political spectrum.

So what explains this alarming resurgence?

The collapse of Europe’s center-right, center-left political consensus plays an important role. As the center has dissolved, the fringes have expanded. The rise of extremist parties has acted like a green light for the Continent’s anti-Semitism, much like U.S. President Donald Trump has empowered racists and white supremacists to speak up on the other side of the Atlantic.

At a basic level, today’s European anti-Semitic threat is physical. France this month reported a 74 percent increase in violent attacks against Jews, and German police announced a 60 percent rise. In a survey addressing more than 16,000 Jewish people in 12 European countries, the EU’s Fundamental Rights Agency at the end of last year found that 90 percent of respondents felt anti-Semitism is growing in their country, and 30 percent said they have been harassed. Over a third avoided going to Jewish events or sites out of fear for their safety.

The United States, too, is standing on the wrong side of this ideological battleground.

The danger goes beyond the physical. Issues that, on the face, have nothing to do with Jews — the migration crisis or a protest movement sparked by fuel prices — suddenly became all about them. Centuries-old stereotypes have reappeared: the conniving Jewish financier, the all-powerful Jewish conspirator accused of buying political influence or acting as a “globalist,” pulling the levers of power in pursuit of enrichment. The common theme: Jew are “others” who do not belong in European society.

The source of this resurgence differs in Western and Eastern Europe.

In the West, the danger comes from left-wing opposition and from the street. In the U.K., anti-Semitism is tearing apart the opposition Labour Party, whose leader Jeremy Corbyn insists the internationally accepted definition of the scourge infringes on his right to criticize Israel. Muslim critics of the Jewish state are also often guilty of extending their criticism to all Jews: When protestors in Malmö, Sweden rallied against U.S. President Donald Trump’s decision to recognize Jerusalem as the capital of Israel, they called for an intifada and promised “we will shoot the Jews.” A day later, during a demonstration in Stockholm, a speaker called Jews “apes and pigs.” And more recently, the broad anti-establishment French Yellow Jacket protests have portrayed Jews as part of a corrupt establishment that oppresses them and keeps them poor.

In the former Communist bloc, the rot starts at the top. Right-wing nationalist politicians propagate anti-Semitism themselves. Many of the region’s governments — led by Hungary — have rehabilitated their wartime criminals and minimized their country’s guilt in the destruction of their Jewish communities.

Adding fuel to the fire is Israel. Instead of criticizing Europe’s revisionists, Israeli Prime Minister Benjamin Netanyahu cozies up to them, justifying his outreach to leaders in Poland and Hungary as a way to counterbalance the European Union’s more Palestinian-friendly Western states.

There may be something to this. But the Israeli leader seems to share with Jarosław Kaczyński and Viktor Orbán an alarming hostility toward human rights, Enlightenment values and the European Union. He has even echoed the Hungarian prime minister’s attacks on Soros.

The United States, too, is standing on the wrong side of this ideological battleground. Like the Israeli prime minister, President Trump favors Holocaust-revisionist leaders in the East over longtime democratic allies in the West. At home, he traffics in anti-Semitic stereotypes. Even so, many American Jews don’t consider themselves to be in danger, and even think they can support Trump without supporting European anti-Semites.

These worrying trends don’t necessarily portend a return to the 1930s in Europe. Most Western European governments not only defend their Jewish citizens, they plead for them to stay. French President Emmanuel Macron responded to a wave of attacks by announcing new measures to tackle anti-Semitism and told Jewish leaders France would recognize anti-Zionism — the denial of Israel's right to exist — as a form of anti-Semitism.

Germany has been similarly vocal in condemning anti-Semitic attacks and has created a new ministry to tackle issues of Jewish life in Germany.

And yet, violent incidents continue to multiply. Unless the political fringes are reigned in again, their severity and frequency will only accelerate. The European Parliament election in May will send an important signal. The big question is: Will the political extremes win, or will the democratic center hold?

Strengthening and protecting Jewish life in Europe will require us to strengthen and protect Europe itself.

As a Jew living in Europe, part of the EU’s reason for being has always been to tame destructive nationalism, and to privilege and protect minorities — allowing its citizens to be proudly and freely Belgian, French, Polish, or Hungarian — and also Jewish.

These values risk coming under serious threat if parties in the political center find themselves outnumbered in the European Parliament and lose control to populist parties that espouse anti-Semitic ideas. Strengthening and protecting Jewish life in Europe will require us to strengthen and protect Europe itself.

William Echikson is the director of the European Union of Progressive Judaism Brussels office and an associate senior fellow at the Centre for European Policy Studies.