Seating is everything in Washington, in politics, at conventions. So it is no accident that the delegation of the District of Columbia is in the nosebleed seats at the back of the arena here in Charlotte. That's where the pariah mayors could pose for pictures without attracting much notice or enthusiasm: former Mayor Marion Barry and current embattled Mayor Vincent Gray. Both are delegates, Gray the chair of the 50-member group. Most attendees barely looked up when the District's mayor slowly made his way up the stairs to the arenas last rows. At 6 p.m., as a rising-star mayor took the podium, Newark's Cory Booker, Gray sat alone, unsmiling.