Pennsylvania Senator Arlen Specter is moving from the Republican Party to the Democratic Party.

That's good news for the Democrats, who are now only one shy of the 60 votes they need to prevent a filibuster in the Senate. (And assuming that Al Franken is finally declared the winner of that drawn-out vote counting in Minnesota, they'll get their 60.) Whether Specter's switch is good for the country, I think, is less certain.

I'm not a big Specter fan. He's certainly more moderate than most of the Republican Party's leadership, but he can be as ruthlessly partisan as any of them.

But Specter had angered hard-right Republicans, and he was facing a tough Republican primary next year - one he might very well have lost. It's not likely that the Democrats will reward his party change by picking somebody besides him as their candidate, so the change is obviously in his own political interest.

Specter says he's moving to the Dems because his party has moved away from him, sharply to the right. That the Republicans have continued to become more conservative is indisputable. But if the few remaining moderates change parties, there'll be fewer voices of reason in the Republican Party, fewer people willing to look for bipartisan solutions to the nation's enormous problems.

Maybe the single-mindedness - and, increasingly, the small-mindedness - of the party will cause it to shrink into relative obscurity. And maybe then, Republicans with a more temperate approach to politics will take it over. That won't happen overnight, though, and it will leave the country with a single, dominant political party.

Other Specter news: The current issue of New York Review of Books contains a strong piece by Specter on the abuse of power by the Bush administration. He has particularly harsh criticism for former Vice President Dick Cheney. And he complains that when he managed to make some progress in reining in executive power, Congress - including Democrats - undid them.

In the article, Specter lays out specific legislation he plans to introduce to undo some of the damage. (He didn't mention his plan to change parties, but obviously he may find it easier to get his legislation passed now.)