This is also a period of rising criticism of Israel, much of it directed at the rightward drift of its own government and some of it even questioning Israel’s very foundation as a Jewish state. We have been and remain stalwart supporters of Israel, and believe that good-faith criticism should work to strengthen it over the long term by helping it stay true to its democratic values. But anti-Zionism can clearly serve as a cover for anti-Semitism — and some criticism of Israel, as the cartoon demonstrated, is couched openly in anti-Semitic terms.

The responsibility for acts of hatred rests on the shoulders of the proponents and perpetrators. But history teaches that the rise of extremism requires the acquiescence of broader society.

As anti-Semitism has surged from the internet into the streets, President Trump has done too little to rouse the national conscience against it. Though he condemned the cartoon in The Times, he has failed to speak out against anti-Semitic groups like the white nationalists who marched in Charlottesville , Va., in 2017 chanting, “Jews will not replace us.” He has practiced a politics of intolerance for diversity, and attacks on some minority groups threaten the safety of every minority group. The gunman who attacked the synagogue in San Diego claimed responsibility for setting a fire at a nearby mosque, and wrote that he was inspired by the deadly attack on mosques in New Zealand last month .

A particularly frightening, and also historically resonant, aspect of the rise of anti-Semitism in recent years is that it has come from both the right and left sides of the political spectrum. Both right-wing and left-wing politicians have traded in incendiary tropes, like the ideas that Jews secretly control the financial system or politicians.

The recent attacks on Jews in the United States have been carried out by men who identify as white supremacists, including the killing of 11 people in a Pittsburgh synagogue last year. But the A.D.L. reports that most anti-Semitic assaults, and incidents of harassment and the vandalism of Jewish community buildings and cemeteries, are not carried out by the members of extremist groups. Instead, the perpetrators are hate-filled individuals.