William A. Jacobsen and Mike Dorf explain the irony.

[I]ronically, Specter’s defection may give Republicans the ability to filibuster judicial nominees at the Judiciary Committee level, so the nominees never get out of committee.

Huh, you say. Here’s the explanation, from Professor Michael Dorf of Cornell Law School at his excellent blog, Dorf on Law, written two days ago before Souter’s retirement was in play:

Does Arlen Specter’s defection from R to D strengthen the President’s hand in Congress? Perhaps overall but not on judicial appointments because breaking (the equivalent of) a filibuster in the Senate Judiciary Committee requires the consent of at least one member of the minority. Before today, Specter was likely to be that one Republican. Now what?

The link in Dorf’s post is to Congress Matters, which has the Senate Judiciary Committee rule:

IV. BRINGING A MATTER TO A VOTE
The Chairman shall entertain a non-debatable motion to bring a matter before the Committee to a vote. If there is objection to bring the matter to a vote without further debate, a roll call vote of the Committee shall be taken, and debate shall be terminated if the motion to bring the matter to a vote without further debate passes with ten votes in the affirmative, one of which must be cast by the minority.

Now this is interesting. Specter could allow a nominee out of committee if Specter was a member of the Republican minority, but as part of the majority, he’s just another vote. Here are the other Republicans: Orrin Hatch, Chuck Grassley, Jon Kyl, Jeff Sessions, Lindsey Graham, John Cornyn, and Tom Coburn.

The weak link is Lindsey Graham, who was a member of the Gang of 14. If Graham says the course, the Republicans may not be able to stop runaway spending, military retrenchment, and an interrogation witch hunt. But Specter may have handed Republicans a gift.

And how fitting that Joe Biden arranged it all by convincing Specter to switch. Thanks, Joe. I’m sure your boss will appreciate your service as he ponders who he will nominate for the Supreme Court.