Barbara Mikulski, Maryland’s senior Democratic senator, announced her retirement this morning in Baltimore. Mikulski, a social worker and community activist, first went to Congress in the 1970s; she was elected to the Senate in 1987 and became the longest-serving woman in the history of Congress in 2012. In this hour of Midday, more on the Mikulski announcement from WYPR’s senior news analyst Fraser Smith and from Washington College political scientist Melissa Deckman. What does her announcement mean for Maryland Democrats, including former Gov. Martin O’Malley, who aspire to higher office?