We still debate the reasons that crime fell in the 1990s. Better policing? Longer jail sentences? An aging population? Removal of lead from the atmosphere? They all may have played a role, along with other factors we are probably missing.

That debate is now academic. Crime has been rising for several years now. The new concern is why, and how we can get it to stop. Again, there are many factors, but the rise of leftist prosecutors who are soft on crime must be at the head of the list.

In my hometown of Philadelphia, crime as a general matter has been getting worse for years, and there are statistics to prove it. Philadelphia, like many big American cities, is experiencing more violent crime than at any point in its history.

Murder rates are a good proxy for violent crime generally, not only because it is the most horrific crime, but because it is harder to obscure statistically. Whether the authorities want to report it or not, whether or not the police get called, it is hard to hide the fact that someone was killed. Looking at that statistic gives us a fair impression of the level of violence in the city more generally.