From the standpoint of many on the left, former President Donald Trump did exactly two good things in office. He supported Operation Warp Speed, which facilitated the development and production of the first COVID-19 vaccines. And in 2018, he signed the First Step Act, a bipartisan criminal-justice bill that shortened federal prison terms, gave judges more latitude in sentencing, and provided educational programming to ease prisoners’ eventual return to the outside world. The best account of how Democrats and Republicans improbably joined forces in the lead-up to this effort to reduce mass incarceration comes from the political scientists David Dagan and Steven Teles. On the left, progressives managed to persuade centrist Democrats that Clinton-era tough-on-crime policies, such as lengthy prison terms for drug crimes and mandatory life sentences for repeat violent offenders, had done more harm than good. Meanwhile, on the right, a group of savvy conservative activists, some moved by Christian notions of forgiveness, reframed mass incarceration as an example of wasteful government spending. With crime hovering around a 50-year low, a vanishingly rare …