Rep. Michael Capuano (D-Mass.), who came in second to Martha Coakley in the 2009 Democratic primary to fill the late Sen. Ted Kennedy's seat, announced Tuesday that he would not run for the seat to be vacated by Sen. John Kerry (D-Mass.) upon his expected confirmation as secretary of state.
"After careful consideration, I have decided not to enter the race for US Senate," Capuano said in a statement. "Instead, I look forward to focusing on the important issues facing the new Congress. My current work in the House, and whatever opportunities the future may hold, afford me the greatest honor of my life, fighting for the citizens of the Commonwealth."
Capuano represents most of Boston and Cambridge in the seat once held by House Speaker Tip O'Neill.
Rep. Ed Markey (D-Mass.) is the only announced candidate for the special election to fill Kerry's seat, expected to take place in early summer. Markey has secured endorsements from Kerry, the Democratic Senatorial Campaign Committee and other top Democrats.
Capuano's decision leaves Rep. Stephen Lynch (D-Mass.) as the main possible challenger to Markey. Lynch is notably more conservative; he voted against the Affordable Care Act and opposes abortion rights. Recently defeated Sen. Scott Brown (R-Mass.), who beat Coakley back in early 2010, has not made any announcement about whether he will seek Kerry's seat, but he took a shot at Markey over his Massachusetts residency earlier this month.
Gov. Deval Patrick (D) has said that he is leaning toward appointing a placeholder to the Senate seat -- someone who would not run but would serve in the interim period between Kerry's appointment and the election.