Who Stops a ‘Bad Guy With a Gun’?

The lengthy police response to a school shooting in Uvalde, Texas, and the death of an armed security guard as part of an attack on a Buffalo supermarket last month have drawn fresh scrutiny to a recurring (and uniquely American) debate: What role should the police and bystanders play in active shooter attacks, and what interventions would best stop the violence?

The debate has moved to Capitol Hill as lawmakers consider gun safety legislation that could increase funding for mental health services, school safety and other measures aimed at keeping guns out of the hands of dangerous...