Hillary Clinton’s record on criminal justice has dogged her throughout the 2016 campaign, thanks in large part to a federal crime bill that she vocally supported when her husband signed it into law in 1994. The law contained many separate provisions, but its overall thrust was to make criminal penalties harsher and to make the justice system less forgiving. Although Clinton has said on the trail that the law went too far and that she now wants to make the criminal justice system less punitive, critics have pointed to her support for the ’94 law as evidence that she is, at heart, a believer in tough-on-crime policies that disproportionately affect minorities.

This week, an essay in the Nationwritten by Michelle Alexander stated that Bill and Hillary Clinton should be held responsible for what we now call our mass incarceration problem, with an astonishing 1.56 million people currently serving time in state and federal prisons. As champions of a law that resulted in billions being spent on “constructing a vast new penal system” that has ravaged black communities, Alexander argued, the Clintons are not deserving of votes from black Americans. The message carries a great deal of weight coming from Alexander, whose 2010 book The New Jim Crow: Mass Incarceration in the Age of Colorblindnesshas proved enormously influential in shaping the national conversation around the need for prison reform. Alexander’s essay reverberated widely, and it would be surprising if Clinton and Bernie Sanders were not asked about it at Thursday night’s Democratic debate.

But how much did Clinton-era policies on criminal justice actually contribute to mass incarceration? Some experts say their impact has been massively overstated—and that the 1994 bill in particular had much less of an effect on the prison population than Clinton’s detractors would have it. One expert who is skeptical of the 1994 bill’s influence is John Pfaff, a professor at Fordham University School of Law who studies prison policy from an empirical perspective. I called Pfaff to discuss the Alexander article, and the degree to which Hillary Clinton can be held to account for mass incarceration. Our conversation has been edited and condensed for clarity.

Neyfakh: According to the Bureau of Justice Statistics, the combined state and federal prison population in the U.S. went from 882,500 at the end of 1992, when Bill Clinton was elected, to 1,394,231 at the end of 2000, when he left office. Referring to these numbers, Michelle Alexander opens her argument by saying Bill Clinton “presided over the largest increase in federal and state prison inmates of any president in American history.” Is that true?

Pfaff: It’s technically true, in that it’s true that during Clinton’s years in office, more total people were added to U.S. prisons than during any other president’s administration. But the U.S. prison population had been growing steadily for almost 20 years before Clinton came into office, and it didn’t seem to grow any faster during his presidency.

It didn’t?

No. In fact, what you see in the prison population is a steady upward trend from 1974 till around 2000, at which point prison growth starts to plateau a bit. ...