Opinion | It’s an Old and Insidious Hatred. And New Yorkers Can’t Stand For It.

In France last year, thousands took to the streets to protest a sharp rise in anti-Semitic incidents.

How beautiful would it be to see thousands of people, Jews and non-Jews alike, walking arm-in-arm through the streets of Brooklyn?

Such an effort is underway, planned for Sunday in Lower Manhattan. Marchers will gather at 11 a.m. at Foley Square, just north of Chambers Street near City Hall, then walk across the Brooklyn Bridge.

The event was planned by the Jewish Community Relations Council of New York and the UJA-Federation of New York, along with other groups. This is a chance for people of all faiths and backgrounds to show critical support for New York’s Jewish communities. Gov. Andrew Cuomo and Mayor Bill de Blasio can help by joining in, coming together in unity to march against anti-Semitism alongside New Yorkers.

Both men, along with many other New York public officials, have already responded with moral seriousness to the rise in anti-Semitic attacks. Mr. Cuomo rightly described the Monsey attack as “domestic terrorism,” and said he would propose a state law to help address the scourge when the Legislature returns to work in Albany this month. Jersey City, where two gunmen killed three people in an anti-Semitic attack at a kosher supermarket last month, is also grappling with how to respond.

In New York, Mr. de Blasio over the weekend said the city would increase police presence in heavily Jewish areas. That’s a sensible step in the short term, given the palpable fear in New York’s Orthodox communities especially. But longer-term, flooding Brooklyn communities with police officers is not the solution, particularly given the history of overly aggressive policing tactics in minority neighborhoods.

The mayor announced a broader initiative in which community groups will meet regularly to help prevent hate crimes. A similar model has shown promise in fighting gun violence in New York. Improving New York’s mental health system should also help. The vast majority of those struggling with mental illness will never become dangerous to others, let alone carry out hate crimes. But some close to Grafton Thomas, the alleged assailant in the Monsey attacks, have said he has long struggled to find treatment for serious mental illness, statements that shouldn’t be ignored.

Other incidents appear to have been carried out by young people, sometimes in neighborhoods with long histories of tensions between Jewish and black and Hispanic New Yorkers. Mr. de Blasio has also committed to implementing anti-hate crime curriculums in the city’s schools, with a strong focus on middle and high schools in communities adjoining Orthodox neighborhoods.