We didn’t always have the evidence we do now. When crime began to spike in the United States in the 1960s, experts were caught flat-footed. Most criminologists thought crime was driven by sociological factors, beyond the influence of the police. They had little to say about how prevention measures short of fundamental economic, educational and social reforms might curb the violence.

This was hardly a message politicians could take to their voters. So legislators came up with their own, simple prescription: crack down, hard. Our nation declared war on drugs, significantly increased policing and quadrupled incarceration.

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Greater incarceration has played a genuine, albeit modest, role in the great crime drop that began in the 1990s. It also brought a terrible cost in human lives. And it has proved ironically self-defeating, undermining the legitimacy that the criminal justice system needs to function effectively. Scholars such as Tom Tyler and Tracey Meares have demonstrated the unique threat to that legitimacy posed by the experiences of African American and Latino men within our criminal justice system.

What has worked? There are no miracle cures, but several approaches are helpful. The right kind of increased police presence in high-crime communities, not least based on evidence from the COPS program of the Clinton years is one element. Both right and left easily equate greater police presence with a more tough-minded approach to law enforcement. In fact, a larger police force is better-equipped to pursue the restrained, community-oriented strategies that are most needed in high-crime communities. We want officers to spend the time it takes to calm a teenager experiencing a mental health crisis. We want police departments to have sufficient manpower to properly supervise officers on patrol too. An overstretched police force in a high-crime community is hard-pressed to meet these challenges on a busy Saturday night, with sometimes tragic consequences.

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Another powerful tool we have: focusing cops’ time and energy in new ways. Scholars such as David Kennedy have demonstrated the effectiveness of “focused deterrence” models in partnership with communities to curb open-air drug markets and gang violence. Richard Rosenfeld, Daniel Webster, Jacqueline Cohen and Jens Ludwig have helped to build an evidence base for “hot-spot policing” and other strategies to reduce gun violence. Crisis intervention teams offer improved models for interacting with people experiencing a mental or behavioral health crisis. Police are trained to avoid physical confrontation whenever possible, to play for time while keeping physical distance to minimize the risk of a tragedy. Democratic presidential nominee Hillary Clinton has publicly embraced many of these strategies.

Evidence-based prevention programs have taught us how to keep many young people from committing crimes in the first place. Chicago’s Becoming a Man school-based counseling and the city’s One Summer Plus youth employment programs substantially reduced violent offending among thousands of young people while addressing other developmental and economic challenges. These programs have become national models after being validated in big, randomized trials.

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Changes to sentencing policy and prison conditions that have bipartisan support can also make the country safer. As David Dagan and Steven Teles show in “Prison Break,” bright-red states have taken significant steps in recent years to reduce their prison populations and invest the savings in alternatives such as drug treatment or smarter probation and parole supervision. Their message all along has been that these measures are not just humane, but also better for public safety than simply pushing the “tough” button every time someone messes up. The evidence supports them, showing that many of the states that have reduced incarceration also have declining crime rates.

Of course, the United States still has a terrible problem with violent crime. Many cities endure rates of violence that undermine our efforts to promote decent and successful community life. Major cities — including Chicago, Milwaukee and Baltimore — reported significant increases in homicide in 2015. Many are having a tough 2016, too. Chicago already has had 500 homicides. The annual toll was 422 only two years ago.

It’s hard to revitalize local economies when residents are afraid to shop at night. It’s hard to improve urban schools when teachers and students fear random violence. It’s hard to reduce child obesity when parents fear letting their children play right outside their front door. It’s hard to establish stable neighborhoods and cities when community violence spurs middle-class flight.

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We’re not going to solve those problems following the plan laid out by Trump. Criminal justice reformers cannot allow the polarization Trump seeks to inspire. A politics of division worsens crime by destroying the cooperation that’s needed and possible today between Democrats and Republicans, between police and communities, across racial and ethnic lines. We can enact reforms that will really make streets safer without the collateral damage of mass incarceration and abusive policing.