Violent crime has risen dramatically over the last few years. While the FBI still has yet to produce systematic data on 2020, the bits and pieces put together through local police departments suggest a shocking increase in the murder rate in many American cities. And so far, it seems that murders are increasing over last year in many places. The Fourth of July weekend in Chicago provided stark evidence of this trend: 19 people murdered and 104 shot, including 13 children among the wounded. To date, murders have increased 13% in the city over 2020, and a whopping 58% over 2019. This is a policy problem of the first order. But if history is any guide, it threatens also to be a political problem for the Democratic Party. Put bluntly, the challenge that Democrats have...