The ninth day of the Hebrew month of Av, “Tisha B’Av,” is the darkest day on the Jewish calendar.

Jews observe it by sitting on the floor, fasting and rehearsing the calamities that have shaped Jewish history: the destruction of the Temple in Jerusalem, the Crusades, the Spanish Expulsion and the Holocaust.

The holiday is the annual reminder that too many chapters of the Jewish story have been written in tears. But this year, our darkest day became even darker.

Tisha B’Av commemorates the tragedies of the past, but last week, the past became the present: After spending the morning at The Jewish Center, the synagogue I lead on Manhattan’s Upper West Side, Moshe Grunhaus, wearing a yarmulke, started to walk home.

He barely made it 200 feet when he was stabbed in the chest by a man who shouted, “Allahu Akbar,” the words with which Islamist terrorists have all too often announced their murderous intent.

The alleged assailant was quickly apprehended by the police. In addition to charging the defendant with assault and attempted murder, the Manhattan district attorney charged him with a hate crime.

Thank God, Moshe survived the attack and is expected to make a full recovery.

But that’s scant consolation for a community that increasingly feels vilified, isolated and unsafe in the city it has called home for many generations.

For the first time in memory, Jewish life in America is beginning to feel like Jewish life in Europe: armed guards, bulletproof glass, security checkpoints and the constant fear that yesterday’s rhetoric will become today’s assault.

What happened last week on West 86th Street didn’t happen in a vacuum.

When public officials repeatedly cast the Jewish community as a stand-in for the actions of the Israeli government, visibly Jewish New Yorkers increasingly find themselves in the crosshairs.

Mayor Zohran Mamdani is patently wrong to pretend he can criticize Israel, and oppose its very existence as a Jewish state, without slurring and demeaning its supporters — specifically, Jews.

My congregants have asked me whether their children ought to wear caps rather than yarmulkes in public.

My dental hygienist recently told me her 10-year-old grandson came home from public school and asked his mother, “Why do we have to be Jewish?”

Words matter. They establish moral boundaries. They shape what people believe is acceptable to say, and, eventually, what people believe is acceptable to do.

The mayor has called Israeli Prime Minister Benjamin Netanyahu a war criminal; he’s falsely accused Israel of committing genocide; he’s alleged that it’s an apartheid state; and he’s used words like “monsters” to describe its backers.

This drumbeat of demonization has helped create a climate in which Jew-haters feel increasingly emboldened.

Last week’s attack was a sobering reminder that reckless political theater invites bad actors to translate hateful rhetoric into actual hate crimes.

The irony could not be more painful. The rabbis famously taught that the Jews’ Second Temple was destroyed because of sinat chinam, baseless hatred.

Neighbors stopped being neighborly. Civility gave way to contempt. Instead of seeing one another as fellow human beings, people instead saw enemies, rivals and objects of suspicion.

That lesson remains painfully relevant. Societies are undone not only by external enemies;  they are weakened from within when contempt becomes fashionable, when disagreement hardens into demonization and when neighbors become caricatures.

Violence rarely begins with weapons. It begins with words.

For the Jewish community, Tisha B’Av has always been about memory. We recount our tragedies not because we relish dwelling on suffering, but because memory creates moral obligation.

It reminds us how quickly incendiary words can become prejudice, how quickly prejudice can devolve into dehumanization and how quickly dehumanization can erupt into violence.

Now the mayor is using his platform to foment the very fractiousness we’re meant to rise above.

He’s called for New Yorkers to protest Netanyahu’s presence when he visits New York in September.

Has he shown equal urgency in protecting the Jewish New Yorkers who become the targets of the passions such protests inflame?

The first obligation of any mayor is the safety of his citizens. Fixating on the policies of a foreign leader while failing to confront rising antisemitism on the streets of New York constitutes mayoral malpractice and risks endangering more Jewish lives.

Our moment demands that people of conscience not only condemn antisemitism but also speak out against rhetoric that endangers Jews — before more violence occurs.

Let’s shine the light of moral clarity across our city before next year’s Tisha B’Av grows even darker.

Yosie Levine is the rabbi at The Jewish Center in New York City.