I can think of a couple legitimate reasons why:
- Since Specter was one of the few moderate GOP senator's left, Obama could count on him to vote for resonable legislation, which would in turn make his proposals seem more bipartisan
- Specter would have likely lost anyway, to a more conservative Republican, who would in turn lose to a more liberal Democrat than Specter. Thus Specter switching sides results in a net conservaite shift
On the other hand, Specter's defection is certainly not good for the GOP:
- He now has no incentive to go along with their crazy shennanigan's and obstructionist policies.
- Once all senators are seated, the democrats now have the 60 votes required to invoke cloture.
- Specter's surprise defection makes the GOP seem [even more] unpopular and incompetant.
Once again I will reassert my conviction that the GOP will become increasingly irrelevant until they entirely reinvent themselves. My guess is that they will come back as a modern invocation of the Goldwater Republicans, which in my opinion, was the only good version of that party in the 20th century.