The filmmaker Ava DuVernay's 2016 documentary 13th made a powerful historical claim pithily encapsulated in its subtitle: "From slave to criminal in one amendment." The argument goes like this: The 13th Amendment's so-called "exception clause," which outlawed slavery "except as a punishment for crime whereof the party shall be duly convicted," effectively converted race-based slavery into race-based incarceration. That thesis has fascinated amateur history buffs, motivated activists, and given rhetorical ammunition to politicians like Bernie Sanders, who explained in an essay for Medium that, "due to an extreme shortage of labor caused by the emancipation of slaves, former Confederate states exploited the legalization of penal labor by incarcerating newly freed black people.” And it forms an important plank of