In his reply to a letter sent from a Koch Companies employee Wednesday, Obama's campaign manager Jim Messina criticized the Koch brothers' Americans for Prosperity Fund and helped advance the ever-growing Koch-Obama spat. The Koch Companies president of public affairs Philip Ellender wrote Messina a letter last week criticizing the president's accusation that the David and Charles Koch are driving up gas prices, and he argues that their AFP fund draws not just from the Koch brothers' fortune but "rather it has tens of thousands of members and contributors from across the country and from all walks of life." Messina swung at that softball, replying Wednesday:

You argue that Americans for Prosperity is a grassroots organization of everyday citizens. But its emphasis on rolling back environmental protections and blocking a clean energy economy appears to be nothing more than an effort to promote the corporate interests of your employers and others who lavishly, and secretly, fund its operations.

Messina's letter is, of course, as much for the media as it is for Ellender. Obama has made use of the Koch brothers in his speeches, casting them as the oil billionaires hell-bent on his defeat. (Or so Ellender points out in his letter to Messina.) So they'll accept any attention paid to their take-down of the Americans for Prosperity fund. But then, so will the Koch brothers who have also allowed surrogates to publicly air their grievances with the way Obama characterizes them in, for instance, Wall Street Journal op-ed from their lawyer. So basically, this is a spat that both parties are happy to have out in public to help bring out support from their various constituents. In other words, don't expect Messina's to be the last letter you see in this less-than-friendly exchange of ideas.