The centerpiece of the bill — the part Bill Clinton ran on as a candidate — was a provision known as the “100,000 cops on the beat” program. In hearings on the legislation, local police chiefs told Congress that soaring crime rates had overwhelmed their departments — officers were spending far too much of their time responding to 911 calls. In response, the bill provided funds for police departments to add personnel and to adopt “community policing” strategies.

Each locality has used the program differently, but in general cities were able to hire more police officers for old-fashioned “walk the beat” assignments. These policies set in motion a reversal of crime trends. Since 1994, violent crime rates have essentially been cut in half. As Bill Clinton pointed out in Philadelphia, the people who benefit most from decreased crime are residents of poor urban neighborhoods. And — crucially for progressives — the reduction in crime has helped restore citizens’ confidence that government can accomplish important goals.

But those benefits have come with two enormous costs. First, far too many young African-American and Latino men have been subjected to unconstitutional or inappropriate stops by police officers. The Black Lives Matter movement is right to demand change in this practice. There is every reason to think that police departments can scale back the use of “stop-and-frisk” techniques substantially and still do their jobs well. The federal government can help protect against the overuse of stop-and-frisk with greater monitoring of local police departments — in retrospect, the 1994 bill should have specifically authorized such oversight.

The second cost is that an unacceptable number of Americans are in prison. This mass incarceration will be much harder to fix because it has resulted from the same “broken windows” policing that has helped to push down crime rates. Beefed-up police departments, pushing officers to be more active, have produced many more convictions and therefore many more inmates.

These people may not be hardened criminals, but taking them off the street nonetheless helps to reduce crime. That is what makes the mass incarceration problem so morally vexing. Bill Clinton diagnosed this issue precisely in a more reflective speech last year: “The good news is we had the biggest drop in crime in history. The bad news is we had a lot of people who were locked up, who were minor actors, for way too long.”

Critics of the 1994 bill gloss over the hard truth that the good news and the bad news are linked, perhaps because a myth has grown up that the inmates swelling our prison population are drug offenders who pose no real threat to public safety. That is not the case. Only about one-fifth of the people entering prison since the 1990s are drug offenders, according to research by John F. Pfaff, a law professor at Fordham University. As FiveThirtyEight.com recently pointed out, if prisons in the United States released every drug offender tomorrow, we would still have the highest incarceration rates in the world (next up: the United States Virgin Islands, Turkmenistan and Cuba). When we talk about “mass incarceration,” we are mostly talking about people convicted of relatively low-level crimes of violence or theft — a stolen iPhone, a street-corner fight, a few-hundred-dollar burglary from a clothing store.

Surely these crimes need an enforcement response. We mustn’t abandon active policing, as some progressive advocates urge. That path leads back to pre-Clinton days, when Democrats left the crime-policy field entirely to lock-’em-up conservatives. To be fair, many progressives understand this. In New York City, for example, a mayor and City Council speaker who have been prominent supporters of the Black Lives Matter movement recently agreed to add 1,300 new officers to that city’s police force, and their police commissioner staunchly defends the broken windows approach.