If it's About the Supreme Court, Then Specter Matters

I've been reading all week about whether or not the Specter switch is that big of a deal. Matthew Yglesias suggests that, in regard to the Souter announcement, Specter as Democrat really is a big deal because the switch covers a lot of ground on the partisan hackometer. See, if Specter has to run against a hardcore conservative challenger in the 2010 GOP primary, then the senator will come out against anybody Obama nominates. But since the switch, Specter is actually in danger of inviting a Democratic primary challenger if he doesn't toe the party line on this one. Pretty interesting math.