What is going on here?

All of these can be isolated incidents, all these times when the president refuses to acknowledge anti-Semitism, refuses to say that Jews were targeted during the Holocaust, refuses to answer a softball question about it but goes postal on the questioner instead. But they all happened within the last few weeks, and they are starting to add up.

There have been threatening phone calls to JCCs and other Jewish institutions, mainly but not entirely in the United States. There have been four waves of those calls so far; twice, the Kaplen JCC on the Palisades in Tenafly has received one of those calls.

Thankfully, no one has been hurt. The calls have been hoaxes — although that is perhaps the wrong word, implying as it does some element of teasing fun. These calls have been cruel tricks, designed to instill fear. They have sent children out coatless on unusually cold days. They have disoriented fragile old people. They have unnerved the community by their pointless, stupid, unmistakable hatred.

There was vandalism in a Jewish cemetery in suburban St. Louis this week. About 180 headstones were toppled. Again, no one was hurt — at least physically. Josh Marshall, a journalist who created and edits Talking Points Memo, writes that his mother was buried in that cemetery. She was born in the United States, the daughter of Jewish immigrants, lived free of anti-Semitism but sometimes felt guilty about that freedom, a continent away from the Holocaust, and died young, many years ago. He still misses her.

This barbaric and pointless vandalism hurts, he says.

“Stones can be replaced and the dead are dead,” Mr. Marshall writes. “But it strikes hard against something deep inside of me, something even over the decades still umbilically connected to her, to think that this barbarity which she was free from in her life, at least physically, would lap up against her in death, even in this very, very muted way.

“We live in troubled times,” he continues. “Hate and barbarity are always with us. But today they are being granted permission to act.”

We must fight it, he adds.

It is important that we realize that we are not the main targets of this hate. We are not Mexican, or Muslim, or visibly foreign. Most although not all of us are white. We blend. But we have to realize that hate is alive once again — not that it’s ever been dead — and that we can hear its dread footsteps shaking the earth, if we listen.

We have to listen. We can’t afford not to listen.

We don’t know why President Donald J. Trump has been so opposed to naming and condemning anti-Semitism, eventually giving it two prewritten sentence fragments in a talk at the National Museum of African American History and Culture. Most of the time he does not denounce anti-Semitism, as opposed to intolerance in general, despite being urged to do so by a gamut of Jewish leaders, including not only the ADL’s Jonathan Greenblatt and the American Jewish Committee’s David Harris, to name just a few, almost at random, but also the ZOA’s Morton Klein, who generally has been loathe to ask for such statements from the president. (To be fair, Mr. Klein and the ZOA since have declared themselves fully satisfied with Mr. Trump’s denunciation, and are strong supporters of the president.)

We know that forthright denunciations of anti-Semitism, like forthright denunciations of racism, misogyny, and other forms of hatred, are necessary. Hatred grows in the dark. Slime accumulates in shadows. Let’s bring it out into the light and disinfect it. We can’t afford not to.