The question in this post's subject might sound dumb: 60 is the key number in the discussion of how Democrats are trying to keep Joe Lieberman in the Democratic caucus of the Senate while still spanking him for campaigning against Barack Obama and other Democrats. Virtually all the discussion I've seen takes the importance of reaching 60 members of the Democratic caucus for granted because 60 is the number of votes you need to achieve cloture and thereby break a filibuster.
But isn't there a serious logical break in that last sentence? To break a Republican filibuster, the Democrats don't need 60 members of their caucus. They need 60 votes.
The important numbers for membership in the caucus are 50 and 51. If you get fifty people in your treehouse, even if the other party controls the White House, you get enough leverage to share the power to organize committees and whatnot. If you get 51 people in your clubhouse, you get to control committees and office space and all that stuff--no matter how your caucus votes on any given bill.
But 60 isn't like that. At the cloture threshold, only votes matter. Lieberman has already shown that he'll vote with Republicans on important bills, so keeping him in the caucus hardly guarantees a 60-vote bloc. Therefore, the nature of Lieberman's leverage with the Democrats must lie in an implied threat to vote one way as a member of their caucus and another way if outside it. In other words, Lieberman's position must lie on a threat to change his votes for reasons other than conscience.
I realize that Senators sometimes vote for reasons other than the dictates of their most disinterested consciences. That said, we're giving Lieberman a free pass by describing his leverage as involving caucus numbers rather than voting.
Unless I'm wrong, and having 60 members of a caucus does confer procedural advantages to the lucky party that achieves it, regardless of votes on individual bills. If that's the case, I would love to hear the details from better-informed readers.