Specter sees the Alito/Roberts problem - He helped get CONSERVATIVES WITH SPINE ON THE COURT.
He didn't help diddly.
He couldn't stop them. On top of that, in exchange for WH support for his reelection Specter made a deal to get those 2 nominees out of committee.
He's done that, but before that and since then, he is a major PITA who sides with the left more often than not.
Specter's world view is not the same as that of most Republicans and not at all that of conservatives. He is a big spending, more taxes, gun grabbing, baby killing Democrat who is a Republican only because the Democrat slot was too crowded when he ran for DA in Philly.
He's never changed registration to reflect his true allegiances and he only does enough good to get "R" votes when the next election rolls around.
Remember this, you can always count on Specter when you DON'T need him.