In one more end-of-presidency act of clemency aimed at prisoners serving long sentences for drug-related offenses, President Obama announced Thursday that he is commuting the sentences of 330 prisoners. He has granted clemency to more people than any president since Harry S. Truman, and Thursday’s announcement was typical of how Obama’s approach to clemency has differed from that of his predecessors: Obama’s clemency is almost always given by freeing people from prison with commuted sentences, not pardoning people after their release. On Tuesday, with less than a week left in office, Obama granted clemency to 273 federal inmates, including Chelsea Manning, the army intelligence analyst who was convicted in 2013 of disclosing sensitive information to WikiLeaks. Manning’s commutation was one…