Like Jay Cost says, the party apparatus almost always supports the incumbent in a primary challenge for the simple reason that the incumbent’s almost always more likely to win the general. That’s why Bunning might be headed under the bus in Kentucky while Benedict Arlen’s still on board. Toomey probably can’t beat a Democrat in Pennsylvania, which makes the question here simple: Would you rather be stuck with Specter for another six years or is the schadenfreude of seeing him go down sweet enough to be worth losing the filibuster?

Cornyn’s made his decision:

“My job as head of the NRSC is to guide the GOP back to a majority in the Senate,” wrote Cornyn in a letter to Pennsylvania Republicans. “I can’t do that without Arlen Specter. With him as our nominee, I can target our campaign resources toward beating Democrats and growing the Senate Republican Conference.”

The implication of those lines is clear: if Toomey is the Republican nominee next November, “campaign resources” may not flow from Washington to Pennsylvania.

Meanwhile, here’s the latest from the guy who’s going to help us build that new “Republican” majority:

The competitive Democratic primary between Hillary Rodham Clinton and Barack Obama last year spurred tens of thousands of Pennsylvania Republicans to switch their registration to Democratic. Specter is openly encouraging them to switch back, even telling a group of retailers he met with Monday in Philadelphia, “I don’t know if there are any Democrats in this room. If there are, I’m going to need you to become Republicans, Republicans at least for a day.”

Head on over to the NRSC’s donation page in case you feel moved to help re-elect someone who’s been reduced to begging Democrats to cross over and vote for him. Exit question: Does this give Steele an opportunity to firm up his own conservative cred? Some of the RNC’s rank and file want to see Specter punished and Steele fancies himself enough of a maverick to flirt publicly with the idea of supporting primary challenges. Why not give money to Specter and Toomey, as a symbolic show of support for the latter? The base would appreciate it, especially in contrast with Cornyn.