CHICAGO (AP) — Pardeep Singh Kaleka has surveyed the landscape of an America scarred by mass shootings.

Seven years ago, a white supremacist invaded a Sikh temple in Wisconsin and killed six worshippers — among them Kaleka's father, who died clutching a butter knife he'd grabbed in a desperate attempt to stop the shooter. Now, whenever another gunman bloodies another town, Kaleka posts a supportive message on social media. Then later, either by invitation or on his own initiative, he'll journey to the community to shore up others who share his pain.

He's been to Newtown, Connecticut. Charlesto...