Senator Arlen Specter, having voted for Obama's stimulus bill, was already a Democrat in reality. But he made it official today and officially switched parties.

Veteran Sen. Arlen Specter, R-Pennsylvania, switched from the Republican to the Democratic Party on Tuesday, Sen. Harry Reid said...

Specter, a five-term Senate veteran, was expected to face a very tough primary challenge in 2010 from former Rep. Pat Toomey, who nearly defeated Specter in the Pennsylvania GOP Senate primary in 2004.

Indeed, I emailed Pat Toomey back in February. I must have been one of many to encourage him to do so since Toomey announced last month that he would run against Specter in the primary.

Apparently the polling numbers were such that Specter realized he was going to lose a primary challenge--the environment in the Republican party is not conducive to liberal members. So rather than face the wrath of Republicans in the primary election--which he'd surely lose--apparently he's hoping that Democrats will save him in the general election. That would, of course, be in contrast to his fellow stimulus supporter Senator Collins who was summarily thrown under the bus by liberals today.

It's certainly a political move by Specter. The primary would have been Specter vs. Toomey and Toomey would have almost certainly won. By becoming a Democrat Specter will be facing the exact same race but will be able to count on Democratic voters which, statistically, can only help Specter. It's like being able to add a bunch of liberal votes to the Republican primary.

It's a little discouraging to read about a Republican switching parties to become a Democrat, but it really should be a source of encouragement: It means the conservative tide is sweeping the Republican party back to its fiscally conservative roots to the point that people like Specter know they can't win. All they can do is become Democrats--which, honestly, is what legislators that voted for the stimulus plan should be.

Obviously Democrats will spin this as being more evidence that the Republican tent is shrinking and moving further right. In fact, Specter himself claims that the Republican party has moved too far to the right and that's why he's bolting. But the truth is that the stimulus plan he voted for in February would have never been acceptable to the Republican party at any point in his senate career. The truth is that this is a strictly political move to save his career.

I guess we'll see how this political calculation works out for him in the general election. Presumably he has received assurances from the Democrats that he will not face a primary challenge... and I suspect that this senatorial race will be one of the most contested in the nation with both sides pouring tons of money into it.