Massachusetts Rep. Mike Capuano (D) will not take on Sen. Scott Brown (R-Mass.) in 2012 and instead will seek a ninth term in the House.

Capuano said in a statement that he’s made the decision “after serious personal reflection.”

“There are several good candidates currently in the race and I am fully satisfied that any nominee from this group will represent Massachusetts effectively in the Senate,” he said. “I look forward to seeking re-election to the House in 2012.”

Capuano, the fiery former mayor of Somerville, Mass., lost to state Attorney General Martha Coakley in the 2009 Democratic primary for the Senate seat formerly held by the late Sen. Edward Kennedy (D). Coakley ended up losing by 5 points to Brown, then a little-known state Senator in the January 2010 special election.

Democrats in Massachusetts see the current field of seven candidates looking to take on Brown as lackluster. Capuano’s decision not to run effectively makes Harvard Law professor Elizabeth Warren, who appears likely to announce her candidacy in the coming weeks, the presumptive frontrunner for the nomination.

Roll Call Politics rates the Massachusetts Senate race a Tossup.