RUTHFULLY YOURS

America’s acceptance of Jews and Judaism is profound, certainly greater than in any other country where Jews have lived in the diaspora. Last year, the Pew Research Center released a poll in which Americans were asked to rate different religious groups by the warmth of the feelings they inspired. The group that received the friendliest response—as measured by a “feelings thermometer” on a scale of 1 to 100—was Jews, who scored just above Catholics and mainline Protestants. (The lowest-ranking groups were Muslims and atheists.)

Even so, when Robert Bowers walked into the Tree of Life synagogue and murdered 11 people, shouting “all Jews must die,” the reaction among American Jews was more shock than surprise. In part, this is because massacres in what should be safe places are no longer surprising in the U.S. If angry, heavily armed men can commit mass murder in kindergartens, high schools, movie theaters and nightclubs—as well as a black church in South Carolina and a Sikh temple in Wisconsin—there is no reason to think that a synagogue would be immune.

But the Pittsburgh massacre was no random shooting, and it seemed to confirm a growing anxiety among American Jews that anti-Semitism is on the rise. According to a widely quoted statistic from the Anti-Defamation League’s annual “Audit of Anti-Semitic Incidents,” the number of such acts increased by 57% from 2016 to 2017.

If you look at the ADL report in detail, however, the picture is more ambiguous. In 2017, anti-Semitic assaults actually decreased by almost half, to just 19 in the whole country. The number of threats made to Jewish institutions jumped dramatically, by more than 100% over the year before, but almost the entire increase is owed to a single individual, an Israeli teenager who phoned bomb threats to dozens of American Jewish schools and community centers. If you take him out of the statistics, there was basically the same level of anti-Semitic threats in 2017 as in 2016.

Even Mr. Bowers’s crime, though it was the worst attack on Jews in American history, is not unprecedented. In 2006, a gunman shot six people at the Seattle Jewish Federation, and in 1999, a white supremacist attacked a Jewish community center in Los Angeles and injured five people, including three children. That the death toll in these incidents didn’t reach the same levels as in Pittsburgh was purely a matter of chance.

The question of whether anti-Semitism is growing should concern more than just Jews themselves, for Jew-hatred is a sensitive barometer of the political health of modern societies. That is because, from ancient times until the founding of the state of Israel, Jews have been a small minority in almost every country where they have lived. Because of the heritage of Christian anti-Judaism, they were also for many centuries a hated and oppressed minority. This means that Jews are not just different—they are a longstanding symbol of difference.

For such a people, it is impossible to flourish in a society that does not embrace pluralism—the principle that difference is not a danger but an asset. European countries were never able to embrace this kind of pluralism. Even when they offered Jews legal equality in the 19th century, they continued to think of Jews as outsiders and, therefore, as threats and rivals. Anti-Semitism was born as a modern political movement in 1879, when Wilhelm Marr founded the League of Anti-Semites with the goal of expelling Jews from Germany.

There is only one country in the modern world where pluralism was part of its political DNA from the start, and that was the U.S. George Washington eloquently defined this value in his 1790 letter to the Jews of Newport, Rhode Island: “For happily the Government of the United States, which gives to bigotry no sanction, to persecution no assistance, requires only that they who live under its protection, should demean themselves as good citizens.”

American history can be seen as a continual struggle to keep this promise—to extend respect to all types of difference and to honor the sanctity of every individual. For Jews, living in such a society has made it possible to flourish in ways that were unimaginable in Europe. They could be Americans without ceasing to be Jews, and they could succeed to the best of their abilities without calling down hatred and envy on other Jews.

Political anti-Semitism, then, is more than an expression of prejudice. It is a declaration of war on American pluralism. There have always been Americans who reject that principle, who desire uniformity of race or religion and treat difference as a reason for fear and hatred. When Robert Bowers referred to Jews on social media as enemies of “our people”—by which he meant the white race—he was invoking exactly the logic of foreignness that motivated the inventors of modern anti-Semitism in Europe.

Such ideas are still considered illegitimate in American politics, but there is no doubt that they are being voiced more boldly today than in the past. In part, that is because of the rise of social media, which has allowed anti-Semites who once would have remained in the shadows to find one another. Only a few hundred racists marched in Charlottesville, but that was enough to transfix the attention of the whole nation.

More worrying is the mainstreaming, in the Trump era, of attacks on immigrants and “globalists,” in particular George Soros. For some Americans today, Mr. Soros plays the same role that the Rothschilds or the Elders of Zion did in earlier generations—a Jewish mastermind who controls world events from behind the scenes. This kind of conspiracy thinking encourages anti-Semitism, even if it is accompanied by explicit disavowals of anti-Semitism.

History shows that, when difference is seen as dangerous, life will become dangerous for Jews—and then for everyone else. After Pittsburgh, American Jews will learn to live with even stricter security measures—armed guards, X-ray machines and concrete barriers. But in the long run, the best protection for Jews is to live in a society of free, diverse and confident individuals—which is what America, at its best, has always tried to be.