The Maryland State and District of Columbia AFL-CIO has decided not to endorse a candidate to replace Sen. Barbara A. Mikulski (D), president Fred Mason Jr. told the Washington Post Tuesday. Mason said a committee of several dozen executive board members and representatives from the state’s five central labor councils interviewed U.S. Reps. Donna F. Edwards and Chris Van Hollen, both Democrats, as well as Republican Richard Douglas. To win support, a candidate would need the backing of two-thirds of the committee members. None of the three cleared that bar. “It happens sometimes when there are two very good candidates,” Mason said of Edwards and Van Hollen. “They’re both good quality candidates, they’ve both represented Maryland [well] in their respective positions. . . . That’s why it was so hard.”