There are a few truths that we should acknowledge, Abraham Foxman said.

Mr. Foxman, who lives in Bergen County, is the director of the Center for the Study of Anti-Semitism at the Museum of Jewish Heritage in Manhattan. He is also the director emeritus of the Anti-Defamation League, where he worked for 50 years, and he is European-born, hidden during the Holocaust. Through each of these experiences, he has gained hard-won firsthand experience of anti-Semitism.

Anti-Semitism always has existed; it is, Mr. Foxman said, “the mother of all hatreds.” It’s always existed, even in the United States; ebbs and flows, dries up, and then bursts its banks. And yes, it is particularly strong now, and has been since the presidential campaign. But the numbers of anti-Semitic acts, even here, always are shockingly higher than most of us realize.

President Donald J. Trump did not react quickly or even particularly appropriately to the spate of bomb threats made to JCCs and other Jewish organizations, or to the vandalism that demolished or harmed about 180 tombstones in a Jewish cemetery in St. Louis. But now he has — last week he issued a statement deploring the bomb threats and vandalism, on Monday his spokesman, Sean Spicer, read a statement condemning the desecration of a Jewish cemetery in Philadelphia — and it is our obligation, as a community, to accept those statements and move on. To do anything else is to politicize a need that should remain above politics, he said.

“People in our community are asking why? Why now? What’s going on?” Mr. Foxman said. “We have short memories.” Statistics show that about 10 to 12 percent of Americans “are infected with anti-Semitism — and that’s about 30 to 40 million people. So we shouldn’t be that shocked that there are phone calls threatening Jewish institutions and desecrations of cemeteries. It happens every time there are social eruptions. It comes to the fore.

“We have to remember that anti-Semitism never has been eliminated, so we shouldn’t be shocked or surprised when we see it. We have tried to keep it down, calling it immoral, un-American, anti-Christian, unacceptable, but we never eliminated it. It continued.

“It has laid dormant in the sewers for a long time, but now some of the sewer covers have been removed. Whenever our society experiences instability, uncertainty, polarization, hypernationalism, nativism, isolationism, that legitimizes prejudice.”

Abraham Foxman

Abraham Foxman

Still, there have been taboos that kept people from letting the words of hatred that boil in their hearts out through their lips, but “The election destroyed the taboos,” Mr. Foxman said.

But the “greatest facilitator of anti-Semitism today continues to be the internet, and with the explosive growth of social media, the superhighway that permits anonymous — and also nonanonymous — anti-Semitism is almost like a new hechsher. It both legitimizes and creates a new means of distribution.”

The question, Mr. Foxman continued, is “How do we combat it? What do we do? From my perspective of 50 years, my greatest disillusionment is going back, after Auschwitz was laid bare for all the world to see what anti-Semitism can lead to, and realizing that the world didn’t come together to develop an antidote, a vaccine, against it, I came to the realization that it always will be there. It will always be a yesh, as the Israelis say. A presence.

“Things have not changed,” he said. “We have to combat it from the outside and the inside.

“From the outside it is critical to have all voices — the political, the moral, the religious, the civic — have all of them heard. To make sure that the community as a whole condemns it. Nobody should misunderstand that Jews are outside the circle of civility. At the same time, we have to engage law enforcement to its utmost, not only to pursue the criminals but to be vigilant about the judicial system. When the perpetrators are captured, they shouldn’t wind up with a slap on the wrist and an order to say ‘I won’t do it again’ three times.”

While we remain vigilant, though, Mr. Foxman said, “we walk a very delicate balance here. We have to take anti-Semitism seriously but we cannot exaggerate it, because if we do, God forbid that Jews do not want to be Jews anymore.”

He talked about a conference, years ago, where he heard an explanation of Jewish survival that has remained with him since then. Where would Jews be in half a century? The scholars on the conference panel asked why the Greeks, the Romans, the Incas, and other great empires collapsed and vanished, while the Jews remained. There was one trait that Jews shared and members of other groups did not, Mr. Foxman said. After they were vanquished, the Greeks had no interest in remaining Greek, and the Romans and Incas felt a similar disinclination to retain their old identities and cultures.

The Jews were different. Even after the monstrous evil that was the Holocaust, once they were liberated, still reeling from the trauma, “The Jews dusted themselves off and said, ‘I want to continue to be Jewish.’” We must hold onto that resilience, he said.

But, Mr. Foxman warned, we should not politicize our approach to anti-Semitism. “It is too serious, too delicate, too important an issue,” he said.

The president acknowledged the anti-Semitism that the country now is experiencing. “And he sent his vice president,” Mike Pence, to Dachau, and to the vandalized cemetery in St. Louis. But, Mr. Foxman said, many Jews saw Mr. Trump’s acknowledgement and Mr. Pence’s trip to be too little and too late. So, Mr. Foxman said, the Jewish organized community, led by many prominent organizational leaders, “persisted and we pressed, to the point where his spokesman, Sean Spicer, said, ‘you can’t be satisfied.’

“I don’t have a problem” with Mr. Trump, he continued. “We are well within our rights to ask the president to condemn anti-Semitism, but once he has condemned it, we have to move on. We have to not badger him about it.

“I still will be vigilant,” Mr. Foxman said. “I will watch. But I am concerned that our issue,” anti-Semitism, “is not hijacked. The atmosphere is so politically charged that everything is seen through that prism.”

That is not at all to say, he added, that anti-Semitism should be the Jewish community’s only concern. It is not. “There are all sorts of other issues that we care about — immigration, social justice, freedom of speech, the separation of church and state. They are very important, but they shouldn’t be conflated with this one.”