WASHINGTON   Pentagon leaker Jack Teixeira pleaded guilty to a military charge of obstructing justice, according to media reports Thursday. Teixeira, 23, a member of the Massachusetts Air National Guard, was sentenced in federal court last year to 15 years in prison for leaking classified US national security documents online. He faces potentially another 10 years in custody for the obstruction charge. He is expected to be sentenced later on Thursday. In remarks to the court ahead of his