Across the country—from Louisiana to Iowa to Massachusetts—so-called “mandatory minimum” sentencing is increasingly out of favor. These are laws that require certain penalties for people convicted of specific drug or firearm offenses. A powerful bipartisan consensus has emerged around the idea that mandatory minimums are ineffective (and expensive) deterrents, as well as racially discriminatory and unlikely to reduce recidivism.

Yet this month in Baltimore, the city council voted 8-7 in favor of …