Even before anything at all was known about Jared Lee Loughner, who went on a deadly shooting spree outside a Safeway in Tucson, Arizona, on Saturday, a narrative was beginning to take shape.

Partisans on the left immediately blamed the Tea Party, Sarah Palin, “talk radio,” and Republicans more generally. That’s regrettable but probably inevitable. Agitators like Markos Moulitsas, whose Twitter feed on Saturday is full of such charges, make fact-free accusations as a matter of course. So he wrote: “Fucking American Taliban” and “Mission Accomplished, Sarah Palin.” He wasn’t alone. Paul Krugman blamed talk radio for a “climate of hate” and Keith Olbermann blamed Sarah Palin and others.