You’ve studied criminal law and policing for two decades. Is crime out of control in American cities?

Crime rates in the United States are at historic lows. Homicide and violent crime, in particular, are less frequent than they were at any time in the 1970s, 1980s, 1990s, or the early 2000s. That’s true almost everyplace in the country, including in most major cities. The homicide rate in Los Angeles is about a quarter what it was in 1990; in New York City it’s about an eighth. There are cities like Philadelphia where homicide rates have recently been ticking up, but those are still much safer places than they were twenty-five years ago. Chicago is an outlier; homicide rates there are almost, but not quite, as high as they were in 1990, and it’s not clear why.

President Trump has raised concerns that undocumented migrants are responsible for a considerable amount of crime in the U.S. Does the data support that concern?

That’s demagoguery. There’s zero evidence that undocumented migrants commit a disproportionate share of crime in the United States, and quite a bit of evidence the other way. The best proof, maybe, is the relatively low rates of violent crime and property offenses in border cities like San Diego, Laredo, El Paso, and Brownsville. Those are places with very high concentrations of noncitizens, including undocumented migrants, and they are strikingly safe. San Diego, El Paso, and Brownsville have lower homicide rates than Des Moines. The rate in Laredo is only slightly higher.

Is there any evidence that refugees, in particular, contribute significantly to crime in the United States?

No. And that’s hardly surprising, given that refugees have always been screened more carefully than other immigrants. Even in countries, like Germany, that are far more welcoming of refugees than the United States, the evidence suggests that refugees are more law abiding than long-term residents.

President Trump signed an executive order last week directing federal agencies to take away funding from self-proclaimed sanctuary cities. New York City Mayor Bill de Blasio said last week that New York would remain a “sanctuary city” primarily because the NYPD depends on and advocates for good relationships with immigrant communities in order to prevent crime. Can you explain why that might be so?

Mayor de Blasio is hardly alone here. Almost any mayor or police chief in a large American city will tell you that the police need the cooperation of immigrant communities in order to fight crime. Effective policing depends on the trust and cooperation of the people served by the police department—rich and poor, native-born and immigrant. The police need witnesses to come forward, and they need people to talk to them about community problems that lead to crime and to work with them in solving those problems. Immigrants aren’t going to trust the police and work with the police if they are afraid the police will help deport them, or help deport their relatives or friends. Charlie Beck, the police chief in Los Angeles, points out that half a million people in his city are undocumented immigrants, and that if the LAPD takes on the role of immigration enforcement it tears apart the fabric of trust necessary for policing. The LAPD doesn’t want to lose federal funds any more than New York does, but Beck says this is a matter of principle, a “core value” that transcends financial considerations.

As you mentioned, Chicago stands out as an exception to crime trends with a violent crime wave that appears tied to gang violence. President Trump held up “stop and frisk” as a crime-fighting method that worked in New York and should be tried in Chicago. Did it work in New York?

It’s important to distinguish the tactic of “stop and frisk” from policies directing how the tactic is employed. Every police department—every police officer—stops people and frisks people without a warrant, based on reasonable suspicion rather than probable cause. That is fully constitutional, and no police department anywhere in the country has ever ceased doing it. The question is how and when to use those tactics. New York City for many years directed its officers to employ the “stop and frisk” tactic in ways that not only were especially aggressive but also, a federal judge concluded, racially discriminatory—and not just because the stops were concentrated in minority neighborhoods. Crime continued to fall in New York after the NYPD abandoned those policies, so no, I don’t think there’s any reason to believe they “worked”; they succeeded only in driving a wedge between the police and minority communities. That’s why the NYPD began to turn away from its old “stop and frisk” policies even before they were under court order to do so.

The President also suggested sending the “Feds” to Chicago. What do you think of that idea?

Well, I’m not sure I would call it a suggestion; it sounded more like a threat. Trump said in a tweet that “if Chicago doesn’t fix the horrible ‘carnage’ going on … I will send in the Feds!”

I don’t think anyone knows exactly what he meant by “the Feds.” The best guess is that he meant the National Guard. If so, that would be a terrible idea even if it came from the local authorities, which it hasn’t. Hyper-militarized policing was one of the worst, most counterproductive trends in law enforcement over the last fifteen years. You don’t earn the trust of a community by rolling armored vehicles down the street.

There is a bigger issue here. The federal government has a critical role to play in ensuring that police departments safeguard constitutional rights, including the right to equal protection under the law. Aside from that, though, law enforcement has always been predominantly a local responsibility in the United States, and there are good reasons for that. First, people in Chicago are the ones suffering from the violent crime there, and they are the ones that will have to live with the consequences of whatever policing tactics are employed. Second, effective law enforcement requires an understanding of, and cooperation with, the local community.

Third, and most important, concentrating power—especially police power—imperils democracy.  That’s not a liberal or conservative idea; it’s a deeply American idea.  J. Edgar Hoover, the founding director of the Federal Bureau of Investigation, was no one’s idea of a civil libertarian, but even he recognized that “[c]entralization of police power represents a distinct danger to democratic self-government,” and that therefore it would be “disasterous” to make “local and state law enforcement subservient to federal jurisdiction.”  The risk of abuse of power, Hoover said, was simply too great.  Trump’s imperious threat to “send in the Feds”—possibly provoked by his feud with Chicago Mayor Rahm Emanuel—kind of proved Hoover’s point.  And that was before the bullying rollout of Trump’s immigration order, and the Administration’s apparent flouting of judicial authority over the weekend.

So how are communities fighting crime? What are the best practices that are emerging?

We’ve known for close to three decades now that the best policing strategies rely on trust, cooperation, and partnership between law enforcement agencies and the communities they serve.  Building trust can be difficult.  And there’s a lot of room for debate about how, exactly, police departments should “partner” with communities:  what kinds of community oversight work best, how decision-making authority should be distributed, and how involved the police should be with things other than law enforcement and crime prevention, narrowly conceived.  Reasonable people can disagree, that is to say, about the best way to build strong and durable ties between police departments and the people they serve—how to make policing a genuine exercise in self-government.  But those are the arguments we should continue to have, and that is the agenda we should continue to pursue.  And one thing is really clear: you can’t build the kind of legitimacy we should want for our police without respect for the rule of law.

David Alan Sklansky is the Stanley Morrison Professor of Law and Faculty Co-Directory of the Stanford Criminal Justice Center. He is the author of Democracy and the Police (Stanford University Press 2008), and he writes regularly about criminal procedure and law enforcement.