The head of the U.S. Office of Personnel Management (OPM) abruptly resigned Tuesday, leaving a void atop a sprawling agency that oversees the federal workforce. "OPM has received the resignation of OPM Director Dale Cabaniss and OPM Deputy Director Michael Rigas is Acting Director, Office of Personnel Management," an OPM spokesperson confirmed in a statement. Cabaniss's departure was unexpected, according to sources familiar with the matter, and was believed to be related to internal conflicts. She chafed at treatment by John McEntee, the 29-year-old head of the office, as well as Paul Dans, OPM’s White House liaison, Politico reported. McEntee...