Let's not make too big a deal out of this. Santorum is practicing what's called Senatorial courtesy. It's against custom to campaign against one's home state colleague in the general, and unheard of to oppose him in a priamry.
There is an upside to this. Even if Specter does get the chairmanship, he will be beholden to Senate conservatives who gave him a chance to prove his loyalty. He will probably support a conservative nominee, and possibly use his influence with 'Rats to win a few crossovers.
As one who has corresponded with Specter's office since 1986 I totally agree. I'll say it again, Lott and Santorum by his right side blocked a real Impeachment trial. Specter wanted a real one but was blocked.
Think about that one.