The Washington Post's The Fix blog reports. (The 60-seat majority assumes that Franken will be seated as the Minnesota senator, but that seems very likely.) Sen. Specter will be running for reelection in 2010. Rick Hasen notes that, "Whether or not Specter formally caucuses with the Democrats, if he actually hopes to win a Democratic primary and be elected, he's going to have to go along with the Democratic program this term," though also that "some conservative Democrats (such as Senator Ben Nelson) likely will hold the Democrats back from enacting a fuller agenda."
Sen. Arlen Specter to Switch Parties, Give Democrats 60 Seats and Thus the Ability To Block Filibusters: