When Donald Trump pardoned Steve Bannon last week, the outgoing president blocked the former White House strategist's prosecution for bilking donors to an organization that claimed to be raising money for a wall along the border with Mexico. When Trump granted a commutation to Craig Cesal, by contrast, he freed a man who had already served 17 years of what was originally a life sentence for repairing trucks that were used to transport marijuana. As those examples reflect, Trump's acts of clemency mixed favors to cronies with relief for genuinely deserving federal prisoners hit with grossly disproportionate penalties. The controversy...