Washington - Senator Arlen Specter, who has served as a Republican in Congress for nearly 30 years, announced Tuesday that he has switched parties, inching the Democrats closer to a super majority in Congress's upper chamber. The Pennsylvania senator's defection brings the Democrats to within one seat of the 60 needed in the 100-seat Senate to overcome Republican attempts to block votes on legislation, and enhances President Barack Obama's ability to advance his ambitious legislative agenda.