The massacre at Pittsburgh’s Tree of Life synagogue last Saturday announced with chilling clarity that a lethal strain of anti-Semitism, long presumed to be peripheral in post-World War II America, had returned with a vengeance.

Harbingers had been appearing for months: the online harassment of Jewish journalists during the 2016 presidential race; the anti-Jewish themes deployed by Donald Trump and his campaign; the painted swastikas, toppled gravestones, neo-Nazi handbills, threats to Jewish community centers, and other incidents of hate that made local and national headlines since the election; and the siege of a Charlottesville synagogue during the right-wing rampage there in 2017.

Yet even those warning signs somehow seemed aberrant, and the public outcry in each case told us that our nation’s underlying commitment to ethno-religious pluralism remained sturdy.

Why such confidence? It is true that over the course of the past 75 years, hard-right anti-Semitic voices were—though never eradicated—significantly sidelined. But such security might also be because some of the worst episodes of anti-Semitic violence in American history have somehow faded from memory. Historians describe physical violence against Jews in America as having been rare—painting the United States, in the words of one authority, as having “known no pogroms.”

The abiding image of America as a haven from the bloody religious violence of Europe, for Jews as for others, reinforces the belief that it can’t happen here. In other words, caught up in an idealized picture of America, we’ve let some of the troubling details drop out of our historical narrative.

... for the first time we have a vessel for Coughlinite ideas, however transmuted, in the White House — raising worries that their darker expression may become common once again.

But according to Stephen Norwood, a senior historian at the University of Oklahoma, anti-Semitism in the United States has been “much more deeply entrenched than most scholars acknowledged.” In a startling academic article from 2003, Norwood amassed considerable evidence to refute this sunny picture of America as a sanctuary from brutal violence. In particular, the article tells the story of a right-wing Irish group called the Christian Front, inspired by the wildly popular radio preacher Charles Coughlin, that regularly menaced Jews—especially in Boston and New York—during the final years of World War II.

Starting in 1942 and continuing for more than a year, Norwood recounts, marauding bands of Irish Catholic youths stalked and assaulted the Jews of urban communities like Dorchester and Mattapan in Boston and Washington Heights in New York, as police officers and even elected officials looked the other way. Harrowing as this episode was, few Americans know of it; it was even omitted from a very good recent list of anti-Semitic incidents that ran in the Atlantic.

The role of Coughlin is significant, as he was a key figure in fostering a particular strain of angry right-wing populism, especially popular among American Catholics, that would organize the darkest impulses of American conservatism for many decades thereafter. Back in the 1980s and 1990s it went by the name of paleoconservatism. Its exponents were fond of conspiracy theories, eager to mobilize the power of the masses against alleged elites, often isolationist, protectionist, and nativist, and either overtly or subtly anti-Semitic in character. In the 1950s, its avatar was Joe McCarthy, the rabidly anti-Communist senator from Wisconsin.

In our lifetimes, it was best embodied by Richard Nixon and Ronald Reagan aide Pat Buchanan, who despite spouting anti-Jewish and racist sentiments was one of the most visible television pundits of the 1980s, 1990s and early 2000s. Its best known spokesman today is probably Steve Bannon—although one could include Trump himself.

The point isn’t that Trump is an anti-Semite (though he has said anti-Semitic things) or that he would sanction anti-Jewish violence (he wouldn’t). Rather, it’s that for the first time we have a vessel for Coughlinite ideas, however transmuted, in the White House—raising worries that their darker expression may become common once again.

The years before World War II were difficult ones for American Jews. On the one hand, this was the era in which liberal ideas about equality spread widely in the United States; looking abroad at the vicious anti-Semitism of Nazi Germany and the Soviet Union, Americans defined their values in opposition to those totalitarian regimes, placing civil liberties, religious pluralism and toleration at the center of the national creed. On the other hand, the Depression brought forth ugly resentments that took anti-Semitic form, including toward President Franklin Roosevelt, whom anti-Semites called “Rosenfeld” and whose policies they called the “Jew Deal.”

Many prominent Americans espoused nakedly anti-Jewish views, including carmaker Henry Ford, whose Dearborn Independent published conspiracy theories about international Jewry in the 1920s, and Charles Lindbergh, who in 1941 claimed American Jews, possessing outsized influence in Hollywood, the media, and the Roosevelt administration, were pushing the nation into war against its interests. In 1939, the German American Bund held a rally of 20,000 people in Madison Square Garden, which was decorated with swastikas and other Nazi iconography (footage of which has been circulating on social media in recent years).

A key figure in fomenting anti-Semitic conspiracy theories was Coughlin, who years earlier supported Roosevelt and advocated vaguely left-wing redistributionist egalitarianism but whose populism steadily took on a bitter, aggrieved and, eventually, fascistic tone. Past the peak of his popularity in 1938, he nonetheless commanded a large, loyal fan base, especially among Irish Americans, some of whom formed the Christian Front, a vigilante group. In 1940, the FBI arrested 13 members of the Front for plotting to bomb the offices of the Forward, the Jewish paper, and to assassinate Jewish members of Congress.

According to Norwood, these arrests didn’t dent the Christian Front’s popularity. By 1942, its members—and toughs not explicitly affiliated with it—undertook a relentless monthslong campaign of physical intimidation, beatings and slashings that probably warrant the name pogrom. In what the New York Post called “an almost daily occurrence,” Jews in Dorchester, Roxbury and Mattapan (and, to some extent, in Jewish neighborhoods of New York) were attacked and beaten on the streets, in parks, with some victims stabbed or disfigured, and some girls having had their clothes ripped off. Gangs robbed Jewish merchants, defiled synagogues and cemeteries, and committed other acts of vandalism. Jewish Girl Scout troops and other clubs had to stop meeting.

To the extent that anti-Semitism has crept into mainstream discourse, it has tended to come from the left—commingling with animus toward the state of Israel.

Jewish residents of these besieged neighborhoods told their elected officials that they were living in “mortal fear.” Some non-Jewish leaders spoke up for them—including Frances Sweeney, a leading anti-fascist in Boston; the black New York City Councilman Adam Clayton Powell Jr.; and New York Attorney General Thomas Dewey, who was assailing the Christian Front in his (ultimately victorious) bid for governor in 1942. But most political leaders shrugged.

In New York, Dewey’s opponent, Democrat John Bennett, was sympathetic to the Coughlinites. Others, such as Massachusetts Governor Leverett Saltonstall and Boston Mayor Maurice Tobin, both liberals, weren’t anti-Semitic but probably feared alienating Irish voters. Even New York Mayor Fiorello LaGuardia, himself half-Jewish, downplayed reports as isolated occurrences—an increasingly untenable claim as the violence mounted.

The police disingenuously wrote off reports as run-of-the-mill juvenile delinquency or even sided with the thugs. In one case, two 17-year-old Jewish boys, Jacob Hodas and Harvey Blaustein, were set upon by a mob and then were themselves arrested and roughed up by the police. All the while, the Catholic Church did nothing, and no major newspaper covered the violence until the liberal New York paper PM finally ran an exposé in late 1943. Pressure then mounted on Saltonstall, the Boston police commissioner was soon replaced, and the violence began to abate.

It’s unclear whether the replacement of the police chief alone caused the violence to cease. (It diminished in New York, too.) The end of the crisis coincided with the war winding down and Americans learning the full nature of Hitler’s plans to exterminate European Jewry. Even though prejudice lingered, explicit anti-Semitism became unacceptable in mainstream politics.

The idea of what historian Kevin Schultz has called “Tri-Faith America,” which had gained currency before the war, came to be widely accepted. And as another historian, Stuart Svonkin has written, groups like the Anti-Defamation League and the American Jewish Committee poured their energies into interfaith programs, educational efforts, and research into the social and psychological nature of prejudice and bigotry, relying on some of the leading social psychologists of the day. One of them, Gordon Allport, whose book The Nature of Prejudice became a canonical work in the field, was sent by Saltonstall in 1945 to give lectures to the Boston police force in what Norwood deems the first-ever training course in prejudice awareness for policemen. These ideas and practices made their way into educational curricula and the broader culture, influencing generations of American children about prejudice and racism. (They should be revived today.)

The intervening years have hardly been free of anti-Semitism, even of a violent kind. But incidents have been sporadic, rarely tied to organized movements. Figures like Pat Buchanan and Joseph Sobran certainly maintained followings on the right (and Buchanan sustained his ubiquitous television presence), although in time they too were marginalized. To the extent that anti-Semitism has crept into mainstream discourse, it has tended to come from the left—commingling with animus toward the state of Israel.

How long the official consensus against anti-Semitism will endure remains uncertain.

Until recently, the most well-known public controversies over anti-Semitism have centered on advocates of black radicalism, such as Louis Farrakhan or Amiri Baraka, or of Islamist terrorism; the attacks of 9/11 in particular prompted essays, like those written this week, prophesying that a dark strain of anti-Semitism had resurfaced. Some left anti-Semitism mirrors that of the right—with conspiratorial thinking, claims of Jewish disloyalty or un-Americanness, and fantasies that Jews will take a peace-loving America to war—just as the far left’s blend of isolationism, protectionism and anti-immigration sentiment finds a reflection in Trump’s international agenda.

Anti-Semitic attacks are on the rise, but it would be premature to say anti-Semitism has returned to what it was in the 1940s. One big difference between then and now is that public officials have unanimously condemned the violence in Pittsburgh and elsewhere. But, we might be moving in the wrong direction. As many have pointed out, Trump’s response has still been grossly inadequate, as he continues to demonize George Soros with tropes out of “The International Jew,” and other Republicans have persisted in running campaign ads and tweeting messages with anti-Semitic overtones. How long the official consensus against anti-Semitism will endure remains uncertain.

Recently, historians of the U.S. have been asking whether core features of the postwar order that seemed solid or even permanent—a mixed-economy welfare state, American leadership in the world, objectivity as the lodestar of journalism—are looking more like products of a passing era, what one scholar called a “long exception.” It’s now an open question whether the taboo against anti-Semitism was a product of that long exception as well.

David Greenberg, a professor of history and journalism and media studies at Rutgers, is a contributing editor at Politico Magazine. He is the author of several works of political history including, most recently, Republic of Spin: An Inside History of the American Presidency.