Well before the facts were known in the Tucson shootings, the usual suspects were busy pointing fingers at 'the right's violent rhetoric' - "...the Tea Party ...", "... Sarah Palin" ... blah, blah.
Glenn Reynolds gathers relevant evidence.
Blazing Cat Fur has more.
Must be a corollary of Godwin's Law at work here. Any leftist discussion inevitably degenerates to a reductio ad Palinum (or Tea-Party-um) ... or somesuch.