Ending an investigation that clouded the tenure of former Senate majority leader Bill Frist, federal prosecutors have decided not to file insider-trading charges against the Tennessee Republican for his sales of stock in a family-owned chain of hospitals. The U.S. Attorney in the Southern District of New York and Securities and Exchange Commission staff sent Frist letters last week signaling that they had closed their joint, 18-month investigation. The letters essentially cleared him of wrongdoing. Frist said in a statement that he "acted properly" and that his only reason for selling stock in his trust accounts was to "eliminate the...