Santorum’s 2004 endorsement of Arlen Specter during his primary fight against Pat Toomey is well-known, but what I didn’t realize was that Santorum had previously endorsed Specter during the 1996 cycle (via Trinko):

And as for the pro-abortion-rights presidential candidate Santorum endorsed, when Specter launched a long-shot bid for president in 1995, Santorum — his fellow Pennsylvanian — was one of his few high-profile endorsements.

The story treats the earlier endorsement as repayment to Specter for supporting Santorum’s Senate bid the year before, but that’s not much of an excuse. Santorum might try to defend the 2004 endorsement of the incumbent Specter in the Senate primary as an example of being an obedient partisan. Reliable partisans were expected to support incumbents faced by primary challengers, and Santorum fell in line. That’s not admirable, but it is not all that surprising. No one can say the same of his endorsement of a moderate Republican’s pro-choice protest candidacy whose main reason for being was to try to marginalize social conservatives.