Once they were rivals. But on Friday, former Sen. John W. Warner, a Republican, made his case for why Virginians should re-elect his Democratic successor, Sen. Mark R. Warner, in November. John Warner said it “is not a good time” for a “flip flop” of Mark Warner’s seat. “We need seniority, and we’ll go to lowest in seniority in the Senate if this man is not re-elected,” John Warner said at the Annual Virginia Political History Project forum at the University of Virginia in Charlottesville. Larry Sabato, director of the school’s Center for P...