Why does DOJ want to drop its case against Michael Flynn?

Two and a half years after former National Security Adviser Michael Flynn pleaded guilty to lying to the FBI about his contact with Russian officials, the Justice Department has asked a federal judge to drop the case against him. Judy Woodruff talks to Neal Katyal, who was acting solicitor general in the Obama administration, and Brett Tolman, a former U.S. attorney for the district of Utah.