PHILADELPHIA — Leon Harris, 35, is intimately familiar with the devastation guns can inflict. Robbers shot him in the back nearly two decades ago, leaving him paralyzed from the chest down. The bullet remains lodged in his spine. “When you get shot,” he said, “you stop thinking about the future.” He is anchored by his wife and child and faith. He once wanted to work as a forklift driver but has built a stable career in information technology. He finds camaraderie with other gunshot survivors and in advocacy. Still, trauma remains lodged in his daily life. As gun violence surged...