Here is a clip from the article, What Specter's switch says about him, the Democrats and our political spectrum:
Democrats will understandably celebrate today’s announcement, but beyond the questions of raw political power, it is mystifying why they would want to build their majority by embracing politicians who reject most of their ostensible views.
Reports today suggest that Democratic officials promised Specter that the party establishment would support him, rather than a real Democrat, in a primary. If true, few events more vividly illustrate the complete lack of core beliefs of Democratic leaders, as well as the rapidly diminishing differences between the parties. . . .Specter is highly likely to reprise the Joe Lieberman role for Democrats: a “Democrat” who leads the way in criticizing and blocking Democratic initiatives, forcing the party still further towards Republican policies. . . .
Arlen Specter is one of the worst, most soul-less, most belief-free individuals in politics. The moment most vividly illustrating what Specter is: prior to the vote on the Military Commissions Act of 2006, he went to the floor of the Senate and said what the bill "seeks to do is set back basic rights by some 900 years" and is "patently unconstitutional on its face." He then proceeded to vote YES on the bill's passage (emphasis added).