A workman knocking on the wrong door. A cheerleader mistaking another car for her own. Small errors can have large consequences in a nation bristling with guns.
A 2011 mass shooting left Gabrielle Giffords, then a Democratic congresswoman, partly paralyzed and unable to speak fluently. She has since built a powerful advocacy group.
In Bristol, residents struggled with the killing of two members of the town’s police force in an outburst of violence that left many questions unanswered.