They all do. Specter isn't the only one guilty of this "crime". I see it happen every time Max Baucus (D-MT) is up for re-election. John Thune did the right thing by exposing Tom Daschle for the Liberal he truly is, and look where it got Daschle.
It's insane to put the most liberal member of the Republican caucus in charge of what is in some respects the most important chairmanship.
But perhaps Rove is being clever. Perhaps they cut a deal with Arlen. Perhaps Arlen is making all this noise as a smoke screen. perhaps when the time comes he'll be waving poms poms for every guy Bush send up to the Hill no matter how strict a constructionist. Perhaps Arlen is therefore being used as a cover - "If flaming liberal pro-abort Arlen likes this guy, how bad can he be?"
If so, Rove better have his cojones in a box in his desk drawer.