The number one job of a bad politician is to get re-elected. (LINK)
Specter was facing a primary fight against Pat Toomey that he was sure to lose. Specter lost public support among Republicans when after telling them how conservative he was to get re-elected, voted for the 1.1 Trillion dollar stimulus bill without even reading it. That was the bill authorizing the AIG/ Fannie Mae/Freddie Mac bonuses and the RAT board that undermines internal ethics procedures in the executive branch (LINK).
Our take, people who vote for bills without reading them have no place in the GOP.
UPDATE: Specter said a few weeks ago that there is one party rule in Washington and switching parties would just make things worse (LINK). Now he has switched parties. Early reports are that when Specter stepped out of his office and made the announcement the Washington press people cheered.