And we should not think that such incredible punishments and incredible rates of imprisonment are necessary for public safety. The precipitous crime declines of the 1990s and early 2000s are among the most-studied and complex phenomena in public life, and to say that “getting tough” made the difference is to dramatically oversimplify the debate.

In fact, the smartest conclusions have determined that rapid increases in incarceration are not in fact principally or even significantly responsible for declines in American crime, and they have long passed the point of diminishing marginal returns. A 2012 Brennan Center for Justice paper found that “increased incarceration has been declining in its effectiveness as a crime control tactic for more than 30 years. Its effect on crime rates since 1990 has been limited, and has been non-existent since 2000.”

I don’t want to oversell this point. It’s not that increased incarceration has no effect on American crime, just that that effect has been increasingly marginal. At the same time, however, it has an immense impact on the millions of Americans who are caught up in the system itself, either as prisoners or as their children, spouses, or parents. The effects on family formation and lifetime earning potential are catastrophic, for example, and can lead to enduring cycles of poverty and inequality.