All this might—I underscore, might—be justified if such prison expansion produced dramatic declines in crime. But while crime has indeed dropped dramatically—it’s about half what it was at its peak in 1991—the best evidence suggests that locking people up is not the primary reason. After spending close to two years testing 14 different potential causes of the reduction in crime, the Brennan Center this year concluded that “incarceration was responsible for approximately five percent of the drop in crime in the 1990s,” and an even lower percentage since then. A report last year by the National Academies’ National Research Council found that “the growth in incarceration rates reduced crime, but the magnitude of the crime reduction remains highly uncertain and the evidence suggests it was unlikely to have been large.” Even a 2004 investigation by University of Chicago economist Steven D. Levitt, who considers increased imprisonment more effective, only found that it accounted for roughly one-third of the crime drop.

Some might still argue that, as public policy, Clinton’s tough-on-crime policies were necessary. Listening to Hillary’s impassioned speech yesterday at Columbia, however, where she talked about seeing “how families could be and were torn apart by excessive incarceration,” it’s hard to believe she agrees.

But there’s a different, and more perplexing, defense of the Clinton record on crime. It’s that even if Clinton’s policies can’t be justified substantively, they were necessary politically. If he hadn’t embraced a “tough on crime agenda,” Clinton might never have become—or remained—president.

In the late 1980s and early 1990s, when crime rates hit their peak, the issue enjoyed a salience in American politics that is hard to comprehend today. And for Democrats, the consequences of appearing soft were devastating. In 1988, the George H.W. Bush campaign’s most effective (and notorious) ad slammed Michael Dukakis for furloughing murderers in Massachusetts. (A separate ad, by a pro-Bush PAC, made African American furloughed murderer Willie Horton a household name). The most important moment in that year’s debates came when Dukakis, after being asked how he would react if his wife was raped and murdered, gave a bloodless, and politically catastrophic, answer. In January 1994, 37 percent of Americans said crime was the most important issue facing the country. And that fall, Mario Cuomo lost the governorship of New York State to a little-known Republican, George Pataki, who had made Cuomo’s opposition to the death penalty central to his campaign.

In 1992, Bill Clinton faced a far tougher electorate than Hillary will this time around. African Americans, Hispanics, and Asians, who constituted almost 25 percent of the voters in 2012, and Millennials, who also lean disproportionately left on cultural issues, were either in school or in diapers. There’s a reason Clinton reminded voters that year that his nickname was “Bubba.” It’s because in 1992, far more than today, a Democrat who didn’t appeal to Bubbas couldn’t win. And in 1992, being “tough on crime” was critical to getting most Bubbas to give a Democrat a second look.