As you know, it takes 60 votes in the US Senate for "closure," which ends a filibuster and allows for a vote. This means that, for any bill under consideration under the Democratically-controlled Senate, the key person is the 60th most liberal vote on that issue. The bill ultimately must be tailored to the desires of that 60th Senator.
As we've seen, even with 60 Senators caucusing with the majority (58 Democrats plus two Independents), and even on a single issue -- like health care reform -- #60 can be a moving target. One day you think it's, say, Ben Nelson or Blanche Lincoln, and then suddenly you discover that it's Joe Lieberman.
But I'm struck by how much of a moving target Senator #60 has been over the course of 2009. So I thought I'd go through a timetable on it for your interest and edification.
Jan. 20: Barack Obama sworn in, along with 57 Democrats and 41 Republicans. Ted Kennedy suffers a stroke; for the next three months he is available only for very important votes. For most closure votes, 4 Republicans are needed; for key votes, 3 are needed.
Jan. 28: Kristen Gillibrand sworn in as 58th Democrat, filling Hillary Clinton's vacancy. Dems need 3 Republicans for most cloture votes, 2 for key votes.
April 28: Arlen Specter switches party affiliation to become the 59th Democrat, and proves to be a reliable Democratic vote. However, from this point on Kennedy never casts another roll call vote. Dems need 2 Republicans for closure.
May 18: Robert Byrd hospitalized, and is only available for crucial votes until after summer recess. Dems need 3 Republicans for most closure votes, 2 for key votes.
July 7: Al Franken sworn in after prolonged recount to become the 60th Democrat. Dems need 2 Republicans for most closure votes, 1 for key votes.
Sept. 8: Ted Kennedy has died during summer recess (Aug. 25); Robert Byrd has returned (although he will periodically be hospitalized in the coming months). Dems need 1 Republican for closure votes.
Sept. 25: Paul Kirk sworn in as the 60th Democrat, as Ted Kennedy's temporary replacement. Dems need no Republican votes for closure.
Interestingly, there have been seven closure votes in the Senate since Kirk was sworn in. Two failed, both related to Appropriations bills. Two passed easily, with plenty of bipartisan support. One -- related to Defense Authorization -- passed with 64 votes, with five GOP crossovers, and Feingold voting nay. One related to an appropriation bill passed with exactly 60, with three crossovers from each party. And, of course, one -- allowing the start to the health care debate -- passed on a straight party-line 60-40 vote.