On a hot Mother’s Day weekend in Atlanta, hundreds of people gathered in Piedmont Park to protest against gun violence. The rally rejected the usual Mother’s Day offerings of flowers and chocolates in favor of something far more urgent: a ban on assault weapons, so that mothers could stop burying their children.

Angela Ferrell-Zabala, Executive Director of Moms Demand Action, which organized the rally, remembers it vividly. Especially the moment after she had given a speech, when she was approached by a man who looked shaken and wore a small pin that read “survivor.”

“He started to weep,” she said. “I held him in my arms. He was the husband of a woman who worked at the medical center where a shooting had taken place earlier that week. She had been killed. This was going to be the first Mother’s Day without her, and they had two young children.”

What struck her the…