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.

Arlen Specter’s party switch is worth celebrating.

An abrasive and arrogant liberal who opportunistically trimmed his political sails in stingy microscopic increments carefully calculated to make himself electable finally has found his natural home in the party made for crooks and liars and statists.

Now Arlen Specter can go and extort special personal concessions from the democrat leadership and betray them on key votes.

Doyle McManus, at the LA Times, thinks the democrats aren’t getting anything terribly worthwhile.

Conservatives dubbed him a RINO: Republican In Name Only. Now he has crossed the aisle to join the Democratic majority, but Specter acknowledged Tuesday that he’ll be something of a DINO. Asked whether he plans to attend meetings of the Democratic caucus, he looked momentarily stricken. “Give me a week to think about it,” he said.

Obama and the Democrats, to win Specter over, offered him an amazingly good deal. The president promised to support him in Pennsylvania’s Democratic Senate primary next year. (Presidents don’t normally intervene in primary contests — at least, not so openly.) Gov. Ed Rendell, the most popular Democrat in Pennsylvania, promised to help too. And Senate Majority Leader Harry Reid of Nevada allowed Specter to keep the 28 years of seniority he has amassed as a Republican — meaning he’ll replace some unlucky Democrat of longer standing as chairman of a major committee.

What do the Democrats get in return? A 60th vote — they hope. …

Specter has always been hard to please. He’ll still be the 60th vote on every issue, just as he was on the stimulus bill — the one who always has a special request before he can say yes. Reid will sometimes wonder whether this was such a good deal. …

That approach, after all, is how the Democrats won so many seats in 2006. Under Rahm Emanuel, now Obama’s chief of staff, they welcomed anyone who looked capable of winning an election, beliefs be hanged.

That’s the party Arlen Specter just joined: the Let’s Make a Deal Party. What it loses in coherence, it makes up in voting power.

And Specter was cheerfully open about the cynicism of his move. He changed parties, the senator said, after looking at the polls and realizing that he couldn’t win the Republican primary. (When was the last time you heard a politician admit that he let polls guide his decisions?) He made a brief reference to the increasing conservatism of the GOP. “As the Republican Party has moved farther and farther to the right, I have found myself increasingly at odds with the Republican philosophy,” he said. But he also made clear this wasn’t just about philosophy; he would gladly have remained a Republican if he could keep his job that way.

But that’s how American politics, in all its non-ideological, market-driven glory, often works. As another great Republican, the late Sen. Everett Dirksen, said: “Sometimes a man just has to rise above principle.”