Sen. Arlen Specter (R-Pa.) is switching parties to avoid a primary fight in 2010, which means the Democrats will have a "filibuster proof" 60-seat majority in the Senate. Except not really.

Specter's switch is obviously a big deal, if only as a stark indication of how inbred and self-defeating the Republican Party has become. Specter jumped ship because he was scared to face Pat Toomey, a Club For Growth-backed Republican who almost beat Specter in 2004 by labeling him a moderate, in another primary. Great job, Club For Growth. You targeted Specter because he was insufficiently Republican. Now he's a Democrat. Win!

Still, Specter's switch doesn't mean that there's anything close to filibuster-proof majority in the Senate. Votes for cloture, which cut off debate and end filibusters, require 60 votes. And on contentious issues, it will be just as difficult for Majority Leader Harry Reid to wrangle those votes from moderate Democrats and Republicans as it was yesterday. Specter has already indicated that on the "card check" legislation, for instance—he opposes it—he will not vote with his new party. There are a host of other issues where Specter, Sen. Ben Nelson (D-Colo.Neb.) and others will buck the leadership when asked to help shut down a filibuster.

A more interesting question is which Democrat is sacrificing his committee chairmanship to make way for Specter? Specter is currently the ranking member of the Judiciary Committee, which is currently chaired by Sen. Pat Leahy (D-Vt.), who will release the gavel to Specter with his cold, dead fingers. But by switching to the majority, Specter is actually losing power at judiciary—being the top Republican is better than being the No. 2 Democrat. So it's unlikely he was induced to switch without the promise of a chairmanship somewhere. Sen. Jim Jeffords (I-Vt.) was given the Environment and Public Works Committee in 2001, when he agreed to caucus with the Democrats, giving them a majority.