BEDFORD, Mass. — A military court-martial convened on Monday for Massachusetts Air National Guard member Jack Teixeira , who was sentenced in federal court to 15 years in prison for leaking highly classified military documents after the most consequential national security breach in years. Teixeira pleaded guilty last year to six counts of willful retention and transmission of national defense information under the Espionage Act. He faces additional military charges of disobeying orders and