The recent anti-Semitic assaults in New York and nearby suburbs have attracted less attention than they deserve and require. Jewish people have been punched, hit in the head with a chair, attacked with a knife and assaulted with a brick. Reliable statistics on hate crimes are notoriously difficult to come by because they tend to be underreported. (Many people would rather forget being spat upon, or having their shtreimel knocked off, or being sucker-punched by a total stranger. And who wants to risk retaliation by people prone to violent hatred?) But we know that Jews are the most frequent targets of hate crimes in New York City and that anti-Semitic crimes there have jumped 21 percent in the past year.

Some of these attacks have been captured on grainy surveillance videos that reveal a ferocious brutality. The goal, it seems evident, is not only to humiliate but also to wound. The attackers are clearly people who, in other times and places, would be prime recruits for a pogrom. In such cruelty and violence are the seeds that could grow into a Kristallnacht.

Anti-Semitism is not a simple or single thing. The hatred displayed against Jews in the neighborhoods of Crown Heights and Williamsburg is different from the bigotry of the alt-right marchers in Charlottesville or the prejudice on college campuses where anti-Zionism is employed as an excuse for anti-Semitism. Jews are sometimes attacked for being secretly all-powerful or beaten because they are visible and vulnerable. They have been demonized as exploitative capitalists and as subversive communists, as warmongers and as disloyal pacifists. The charges may be inconsistent or insane.

But there is a common thread in the varieties of anti-Semitism: a determination to blame the other. Through all of Western history, Jews have been an entity on which many non-Jews projected their anger, resentments, fears and venom.

The level of anti-Semitism has always been a kind of test — a measure of a nation’s social health, or the lack of it. When the rights of Jews are violated, all human rights are insecure. When Jews and Jewish institutions are targeted, all minorities have reason for fear.

By this measure, we have a society that is growing sicker. And one of the main reasons is not a mystery. There is a progression that leads from polarization to contempt to dehumanization. And the United States has a variety of leaders who provide permission for prejudice. When a member of the D.C. Council, Trayon White Sr. (D-Ward 8), blamed a snowstorm on “the Rothschilds controlling the climate to create natural disasters” — that was the normalization of conspiratorial anti-Semitism. When an American congresswoman, Ilhan Omar (D-Minn.), suggested that support for Israel is “all about the Benjamins” — that helped to keep an anti-Semitic trope alive for a new generation. When an American president, Donald Trump, found “very fine people” among the Charlottesville marchers chanting anti-Semitic slogans — that was the mainstreaming of alt-right hatred.

This is not to argue that Trump is personally anti-Semitic. How in the world would I know? And I recognize that the administration has taken steps against campus anti-Semitism. But by flirting with extremists — remember Stephen K. Bannon hoping to make Breitbart into a “platform” for the alt-right? — Trump’s political movement has extended its political coalition into the anti-Semitic fever swamps. And when members of that coalition speak of defeating the “globalists” and exposing the secret machinations of George Soros, it is reasonable to discern echoes of anti-Semitism. Any political ideology premised on preserving cultural “purity” is vulnerable to anti-Semitism, because Jews have so often been considered cultural outsiders.

What can be done about so ancient and durable a plague? Plenty. When anti-Semitism emerges as hate crimes or violence, as in New York, there must be a concerted community response: aggressive prosecution by police and aggressive condemnation from political leaders. When anti-Semitic tropes crop up in our discourse, they need to be effectively marginalized. And all these efforts become more powerful when we are willing to criticize anti-Semitism within our own ideological tradition — conservatives confronting problems on the right and liberals criticizing problems on the left — rather than locating the problem mainly among our opponents. When the charge of anti-Semitism is used as a political weapon, it ceases to be a shared moral imperative.

Effectively opposing anti-Semitism is not only a moral task, but it is ultimately a moral task. The virus of bigotry is defeated by a healthy cultural immune system, defined by the prevalence of tolerance, mutual respect and basic decency. And all must be carefully taught.

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