But I'm going to take the slightly contrarian position, that this is not the greatest news for the country as a whole (at least in the long run). Or, more accurately, the real meaning of Specter's switch bodes very badly for the country as a whole.
Obviously, Specter will be invaluable in pushing health care reform along; he will be a staunch supporter of the President's economic platform; he will be a crucial vote in stopping filibusters; and Specter has always been a liberal (and, in my opinion, very sound) voice on issues like torture, stem cell research, a woman's right to choose, etc.
And maybe all of these issues trump what I'm about to say. But, damnit, Arlen Specter was the only Republican in the Senate that I actually liked!
I don't think it's healthy for our country to be a one party system -- even if it's the party I happen to agree with. There is a crucial role for the Republican party during a Democratic administration. The GOP should be critical; it should be sensible; it should stop Democrats from having their way all the time; it should be a moderating force.
And Arlen Specter should be a Republican.
I don't always agree with what he has to say, but he is a very rare voice of sanity. The GOP should not be a religious party; it should not be about abortion (or solely about abortion); it should not have a monarchical view of executive power. It's sole economic agenda should not be tax cuts. In short, the GOP should have more people like Specter -- not fewer. The fact that Specter couldn't take it any more speaks really badly for the state of the GOP as a whole.
The GOP was once the party of Lincoln and Teddy Roosevelt. I don't know what it is today but a barren wasteland of talk radio wingnuts and religious freaks.
That being said: Welcome to the family, Arlen!