On Friday, Rolling Stone published an op-ed from artist John Legend, which was also an open letter to the soon-to-be-departed president. The piece focuses on the prison sentences of non-violent drug offenders in federal prisons, and their need for justice. It's a cause Legend has taken up previously, as he watched his own mother land in prison after struggling with drug abuse. Legend points to Obama’s unprecedented record on commuting sentences across his presidency, which is true. Obama has commuted more sentences than any president in history, doing a small part to combat the problem of the massive prison population in this country (the United States keeps more people locked up than any nation on earth). Just last month, Obama commuted the sentences of another 98 inmates, bringing his total to 944, a number that includes 324 life sentences. But Legend asks Obama to press the gas on thousands more cases before he leaves office. In particular, he points at the sentencing difference between crack-rock and powdered cocaine--a rift repeatedly shown to be policy that unfairly targeted minorities and the poor. Legend writes: An estimated 36,000 non-violent drug offenders housed in federal prisons have sought relief under your clemency initiative and it is unclear how many of the remaining cases will be reviewed before you leave. As the Surgeon General noted, drug addiction is not a moral failing but a chronic health issue deserving of our compassion. What is a moral failing, however, is the War on Drugs and America’s addiction to incarceration which has not increased safety but needlessly torn families apart. In 2010, Congress signed into law the Fair Sentencing Act, which greatly reduced the sentencing disparity between the two forms of the drug--but that leaves thousands still behind bars, prosecuted under the old laws. Legend writes that of the 36,000 cases under review for federal clemency, around 5,000 of those are regarding this difference in sentencing. As a solution, Legend implores the president to make "categorical" clemency, on the grounds that bipartisan voters are in favor of ending the war on drugs. Read Legend's full letter to Obama here.