President Obama knows something about being a low-level, nonviolent drug offender, such as the kind the Justice Department today exempted from harsh mandatory prison sentences. In a sense, he was one himself once, although the young Barry Obama was never arrested or charged with a crime. Obama wrote openly in his 1995 memoir, “Dreams From My Father,” about using marijuana and “maybe a little blow” during his high school days in Hawaii in the 1970s. Biographer David Maraniss reported that Obama was even a pot-smoking trend-setter and leader in the “Choom Gang.” But decades later, openly reflecting on the “stupid”...