Twelve years ago, officials in Vallejo, Calif., reluctantly took a step that activists are now urging in cities across the country: They defunded their police department. Unable to pay its bills after the 2008 financial crisis, Vallejo filed for bankruptcy and cut its police force nearly in half - to fewer than 80 officers, from a pre-recession high of more than 150. At the time, the working-class city of 122,000 north of San Francisco struggled with high rates of violent crime and simmering mistrust of its police department. It didn't seem like things could get much worse. And then they...