(Sen. Barbara Mikulski, D-Md, center, speaks about the recent Metro subway fire earlier this month, as Sen. Mark Warner, D-Va., left, Sen. Ben Cardin, D-Md. center right, and Rep. Eleanor Holmes Norton, D-D.C. wait to speak.) Sen. Barbara Mikulski, the longest serving woman in the history of Congress, is announcing her retirement, Democratic officials say. The 78-year-old Maryland Democrat, now in her fifth term, is set to make a statement at a news conference in Fells Point in Baltimore later Monday. Her retirement could set off a race among potential candidates to succeed her, including Rep. Chris Van Hollen and...