‘The streets are gone,” Dean Angelo, president of the Chicago police union, told me last month. The night before, Aug. 14, a Chicago police officer’s son had been killed in a shooting while sitting on his family’s porch, one of 92 people killed in Chicago during the worst month for homicides in the Windy City since July 1993. The August victims who survived included 10-year-old Tavon Tanner, shot while playing in front of his house (the bullet ripped through Tavon’s pancreas, intestines, kidney and spleen); an 8-year-old girl shot in the arm while crossing the street; and two 6-year-old girls.

On...