WASHINGTON — The former second-ranking officer in the United States military, retired Gen. James E. Cartwright of the Marines, is a target of an investigation into the leak of classified information about American cyberattacks on Iran’s nuclear program, a person familiar with the investigation confirmed Thursday night. The leak investigation, being carried out by the United States attorney for Maryland, Rod J. Rosenstein, was announced by Attorney General Eric H. Holder Jr. after articles in The New York Times described an ambitious series of cyberattacks under the code name Olympic Games that were intended to slow Iran’s progress toward a...