Much of my research and writing has concerned World War II, and as a result I try to steer clear of discussing Hitler or Nazis in any context other than that era. Use either word in the context of contemporary politics at your peril: Invoking them almost invariably has the effect of trivializing monstrous crimes of the past in the service of scoring cheap rhetorical points—and cutting off all rational discussion.
Yet at some point most of us make exceptions to the rules we impose on ourselves. This is mine: What we are witnessing today in the surge of poisonous anti-Semitism around the world, particularly in Europe, would have delighted Hitler and his Nazi followers.
Cloaked in the garb of humanitarian concern for the Palestinian people, anti-Semitism is gushing with such ferocity that the power to shock diminishes daily.
That makes it easy for the far right, the far left, and a lot of people in between to attend rallies where others chant "Hitler was right!" and "Death to Jews"—even if they don't do so themselves.
That makes it seem almost natural that synagogues or individual Jews are once again being attacked in Germany. Police in Berlin had to rescue a Jewish man from pro-Palestinian protesters at one demonstration last month, and at another, according to news reports, protesters chanted "Jew, Jew, cowardly pig, come out and fight alone." Or almost natural that in the Netherlands an outpouring of threats against Jews has prompted many to remove identifying symbols like mezuzas from their doorjambs. Or that in France, amid violent demonstrations and constant harassment, Jews seem more at risk than they have at any time since the German Occupation.
The hateful atmosphere makes it seem almost natural that last week brought news reports about a Belgian doctor refusing to treat an elderly Jewish woman with a fractured rib, later justifying his behavior by saying he had an "emotional reaction." His advice to her son, who called on a medical hotline: "Send her to Gaza for a few hours and she'll get rid of the pain."
In Malmo, a city in southern Sweden with a large Muslim-immigrant population, a synagogue was vandalized on Saturday, and a rabbi and a member of his congregation were assaulted with objects hurled from two cars at different times on the same day. Such incidents are not unusual there.
True, German, French, Italian and other leaders have spoken out against such behavior, building on a long, praiseworthy postwar history of trying to avoid any repetition of the past. The scale of current anti-Semitic attacks is still a very long way from the hatemongering during Hitler's rise.
But are Jews supposed to feel reassured when the level of hate keeps rising? How are they supposed to view those who sign ringing denunciations of Israel for "genocide," casting Israelis as the new Nazis, without bothering to put a smidgen of separation between themselves and those who openly celebrate the killing of not just Israelis—men, women or children—but of any Jews anywhere?
For those who find solace in the idea that the anti-Semitic eruptions in Europe simply reflect Muslim immigrants' anger with Israel, think again. The European far right has a long tradition of anti-Semitism, even if now the right's ire tends to be focused on those same Muslim immigrants.
A poll in France last week showed that Marine LePen, the leader of the National Front, would be the winner if her country's presidential elections were held today. She has worked hard to distance herself from the anti-Semitism displayed by Jean-Marie Le Pen, her father and predecessor as party leader. She projects a more moderate image, but there is little evidence that National Front's core has changed.
On the European left, virulent anti-Israeli sentiment veers regularly beyond opposition to particular Israeli policies and actions into barely camouflaged anti-Semitism. This is very much in keeping with the habits of communist countries during the Cold War, where "anti-Zionist" campaigns were code for targeting Jews.
We tend to forget that Hitler and his followers had moments when they professed a desire for peace and claimed that warnings about threats to Jews were exaggerated. The Nazis assured foreign diplomats that attacks on Jews in the early 1930s were isolated incidents, blaming them on overzealous supporters. Much of the world took those naked lies seriously—and did nothing.
Today, more needs to be done about resurgent anti-Semitism than the general excoriations of it in recent weeks. European leaders should directly and forcefully address the radicals—along with those of the left or right who march beside them—in immigrant communities where anti-Semitism has flared. Preventive policing measures should be stepped up, with any violent behavior—such as the torching of buildings and cars, as occurred in France last month—bringing a stronger police response than we have seen so far.
The Obama administration has repeatedly expressed its unhappiness with Israeli actions, but the president has not prominently addressed the subject of rising anti-Semitism in Europe, much less its pervasiveness in the Muslim world. For that matter, he also has had remarkably little to say about the escalating attacks on Christians in Africa and the Middle East.
Words matter, and the lack of words can matter even more—as was chillingly evident in the 1930s. It is time to speak loudly and clearly.
Mr. Nagorski, a former Newsweek bureau chief in Berlin and Moscow, is the author of "Hitlerland: American Eyewitnesses to the Nazi Rise to Power" (Simon & Schuster, 2012).
