Gun violence is not an abstract concept for Rabbi Joel Mosbacher. His father, Lester, was shot dead in 1999 as he opened up his check-cashing business on Chicago’s South Side. Rabbi Mosbacher, who had been ordained just six months earlier, struggled to make sense of the murder, even as well-meaning friends struggled to find words of comfort and support.

“Some were helpful, others less so,” he recalled. “Someone said ‘This will make you a better rabbi.’ Well, I’d rather be a terrible rabbi and have my father back.”

A young man who had run errands for his father was arrested and tried for the murder, but was ultimately acquitted. For years, Rabbi Mosbacher quietly dealt with his family’s grief. But five years ago he started telling his story as part of a national campaign by clergy and civic-minded residents to enlist public officials — whose law enforcement agencies are major gun buyers — to pressure gunmakers into developing safer technology and crack down on dealers whose weapons end up in criminal hands.

Rabbi Joel Mosbacher, of Temple Shaaray Tefila on the Upper East Side, is co-chairman of a national campaign to get law enforcement and investors to use their purchasing power to nudge gunmakers to take steps to curb violence.

His coalition’s work has been vilified by the National Rifle Association, which considers them “European style socialists.” But he has been buoyed in recent days as major retailers announced they would stop selling assault-style weapons and raise the age of purchase to 21.

“For Dick’s to pull AR-15’s off the shelves, or Bank of America and BlackRock saying they will ask different questions of manufacturers, or Delta not giving discounts to the N.R.A. shows that corporations recognize they have power,” said Rabbi Mosbacher. “We’re now going to double down on that strategy. We’ve been waiting impatiently. But now is the time.”

He had been certain the time had come in December 2012 when 26 people — mostly first graders — were killed at Sandy Hook Elementary School in Connecticut. He and other clergy started meeting with public officials in New Jersey, where he led a suburban congregation, in anticipation of big changes they just knew Congress would enact after the massacre.

They were wrong.

Rather than wait for new laws, he and his colleagues with the Industrial Areas Foundation wondered who else had power. That’s when they realized that corporate and customer pressure might accomplish what Congress could not by targeting the industry’s bottom line.

The resulting national campaign, called “Do Not Stand Idly By,” has so far enlisted public officials in 124 municipalities who have agreed to use their influence as major customers to urge gun manufacturers to explore “smart gun” technology that renders the weapon useless if picked up by someone besides its owner. They also want gunmakers to tighten distribution networks and crack down on the approximately one percent of legal dealers whose weapons disproportionately turn up at crime scenes.

Rabbi Mosbacher, who now leads Temple Shaaray Tefila, a reform congregation on Manhattan’s Upper East Side, serves as co-chairman of the campaign along with the Rev. Anthony Bennett, pastor of Mount Aery Baptist Church in Bridgeport, Conn. Their partnership is not an accident, but an affirmation that gun violence is not limited to poor or minority communities, which have struggled for decades to stop the killings.

“People knew Connecticut because of Sandy Hook,” said Mr. Bennett, who has had several relatives become victims of gun violence. “But me and so many other pastors have to do too many funerals, deal with too many mothers who have to pick up the pieces after their children die, and see too many family members killed because of illegal guns.”

Rather than pressing for outright divestment, the campaign’s strategy depends on staying engaged with the industry, government customers and investors. The campaign is convening a group in the coming weeks to develop a set of guiding principles for investors, akin to the Sullivan Principles, a code of corporate conduct developed in the 1970s in the fight against apartheid.

The recent moves by retailers and N.R.A. corporate sponsors have reaffirmed their commitment to leverage purchasing and investor power, even if manufacturers seem reluctant or if the gun lobby blows the dog-whistle of “European-style socialism.” Every reaction, for good or bad, dictates their next action.

“Corporations can play such a big role,” Rabbi Mosbacher said. “They have power well beyond what a few imams, rabbis and ministers have. And they can use their power without any more laws being passed.”

But, as some officials have asked, will it prevent the next mass shooting, given that there are already enough weapons out there to arm every American?

“I can’t promise that,” he said. “Not with 300 million guns in this country. There is no magic solution, but does that mean we shouldn’t try to turn the tide?”

Rabbi Mosbacher has come a long way since that day when a gun ended his father’s life. And while he speaks with urgency about the need to continue pressing for change, one feeling has stayed constant.

“I, like most people hopefully, have learned from the joyous and challenging moments in my life,” he said. “That said, I would give everything back — all that growth I found — to have my father back.”

David Gonzalez for the NY Times