Tensions are running high between guards and inmates at a D.C. jail housing many of the defendants in Jan. 6 cases, with at least one of those prisoners alleging that he was brutally beaten by correctional officers. For weeks, Capitol riot defendants being held in Washington have complained that they are locked in their cells with virtually no human contact for 23 hours a day. But a startling, graphic account offered publicly in court on Tuesday by one such inmate, Ronald Sandlin, went further: alleging that guards have subjected those charged in the Jan. 6 events to violence, threats and...