Mass shootings and violence killed and wounded people across the U.S. over the weekend. The shootings happened in cities and rural areas alike. Bullets flew in Idaho and Washington state as well as Chicago, San Francisco, Philadelphia and Los Angeles County. The toll included a state trooper who was ambushed in central Pennsylvania. The shootings follow a surge in homicides and other violence that accelerated during the coronavirus pandemic. Experts disagree over causes. It could be due to the prevalence of guns in America. Professor Daniel Nagin at Carnegie Mellon University says disputes that used to be resolved with fists are now played out with firearms.