Congress: What is filibuster-proof?

Even if the Democrats don't get to 60 in the Senate, the Washington Post writes that they might be able to obtain a filibuster-proof majority for matters like health-care programs, immigration, judicial nominations, and voting rights for DC. "Democrats are counting on moderate Republicans such as Maine Sens. Susan Collins and Olympia Snowe, who have tilted leftward on issues such as Medicare spending and the Iraq war, to provide the votes to block a filibuster… Other potential swing votes are Sen. Arlen Specter (R-Pa.), whose socially liberal views make him a prospective Democratic recruit on spending matters and Obama's judicial nominations, and Sen. John McCain (R-Ariz.). … "Senate Democrats, however, must watch their right flank as they craft more sweeping initiatives. Sen. Ben Nelson (D-Neb.) has supported the Bush White House on many tax and budget issues this decade, and a quartet of Democrats elected in 2006 and 2008 – [Mark] Begich, Robert P. Casey Jr. (Pa.), Jon Tester (Mont.), and Mark ... (link)