Last fall, on the worst day to take a helicopter ride above the city of Portland, Oregon, in months, I climbed into a Robinson 44 chopper and soared above my adopted City of Roses. The bird roared nimbly from the roof of the headquarters of Portland’s Police Bureau, the understaffed agency that has found itself a focal point of all the grown-up, big-city problems a town known to the nation for much of the last two decades as the quaint “Portlandia” now faces: a soaring homicide...