Hei Lun of Begging To Differ wonders why conservatives are so worked up over the Specter-Toomey showdown in Pennsylvania. At some level, I suppose it’s the question northern liberals had to ask themselves in the 60s and 70s: do we continue to support conservative southern Democrats, and thereby retain our numerical superiority in Congress and keep the tent “big,” or do we follow our principles and try to get northern-style liberals to win the primary—and risk losing our majority by getting outflanked by the Republicans in the general election.

That said, a Specter defection to the Democrats would only be harmful to the GOP if it was a trigger for defection by the other northeastern Republicans (and therefore tipped the balance in the Senate), and the strategic calculus for Bush is such that the Olympia Snowes of the world will wonder—quite rightly—whether they would be next on the ideological purity “hit list” if Bush had endorsed Toomey over Specter.

On balance, I think both parties benefit from having moderates on their rosters—both for the public relations benefit of being able to claim something is “bipartisan” (a label that the media will apply to any legislation that has even one across-the-aisle supporter) and because they allow the parties to be competitive in areas that they otherwise wouldn’t be; Santorum-style conservatism may be viable for both Senate seats in Pennsylvania (though I suspect many Pennsylvanians think one Santorum is plenty), but it wouldn’t fly as well in other swing states.