The reaction in some quarters of the Left has been less than welcoming to Arlen Specter’s flip to the Democrats. Jonathan Chait of the New Republic weighed in quickly with a post on the Plank titled “Unprincipled Hack,” in which he states: “I think it’s pretty clear that Specter is an unprincipled hack. If his best odds of keeping his Senate seat lay in joining the Communist party, he’d probably do that.” Too true.

Chait ponders whether rank and file Democrats will buy into a corporate merger with this longstanding Pennsylvania “moderate” institution, and states that any Democrat, not just Specter, would beat Pat Toomey next year. Maybe. Having done the Dems a service by increasing their majority to a pro-Obama, veto-proof 60 votes, Specter will have ceased to be of interest to Democrats. So how long will it be until a Democratic challenger to Specter emerges? Left-wingers and pro-choice extremists held their noses and loyally backed a pro-life Democrat like Bob Casey against Rick Santorum in 2006. It is arguable, as Chait hints, that they will not do the same for Specter. Once the Left starts tearing into him on behalf of any Democrat who has the temerity to oppose him in a Senate primary next year, Specter will think back fondly on the largely civil critiques of his positions that came from the conservative wing of the Republican Party.