(Bloomberg) -- Richard Ausness, a professor and the University of Kentucky School of Law, and Leo Beletsky, a professor at Northeastern University Law School, discuss President Trump's Thursday announcement declaring a national emergency over the opioid crisis, which comes one day after Purdue Pharma was targeted by federal prosecutors over the marketing of controversial opioid painkiller OxyContin. They speak with Bloomberg's June Grasso and Greg Stohr on Bloomberg Radio's Bloomberg Law.