Politico: So, just from what you’ve studied for such a long time, what do we know has worked in other cities? If Trump really were serious about solving Chicago’s crime and gun violence problem, what should he look to first?

Pfaff: I think there’s been some evidence that careful, targeted deployment of police shows a fair amount of promise. And things that try to integrate policing with broader social services as well. One program that’s gotten fairly strong reviews—it’s been tried out in many cities and like any program, it failed in some and succeeded in others, but if you look at it overall seems effective—is a program called CeaseFire, and idea behind CeaseFire is what they call “targeted deterrence.” You sit down with those people that are most responsible for lethal violence in that city—so it’s not just identifying members of street gangs, it’s taking the two gangs that are feuding with each other and talking to those ones—and you give them a choice. You say, If this violence continues, we are going to crack down on you really hard collectively as a group. But if you don’t [continue], we have various members of city social services here with us, and they’re willing to work with you to get drug treatment, alcohol treatment, education, housing help, job help. So they know, we’re not just going to threaten you with deterrence, we also want to help you on a different path if you want to do that. It also brings in senior people in the community, so it’s not just city police and city officials saying don’t do this—it’s people who hopefully these young men look up to and respect. So that’s been shown to have an effect.

Another program that’s been shown to have an effect—not a huge effect but overall effective—is what’s called Hot Spot policing. Again, you focus on the geography of where crime is happening, and you deploy police to focus on those areas. That seems to work, and it works in a way that seems not to just place crime elsewhere. One complaint about Hot Spot policing is that if all the crime is on First Street and you flood First Street with cops, crime will just shift to Second Street. But you don’t see that—actually crime goes down on First and Second Street in response to Hotspot policing.