Liberal news sites like the American Prospect are blocking the Web ads purchased by the Obama campaign over the increasingly common use of ad-buying "middlemen" like AOL's or Google AdSense. Craig Timberg reported on the details of the dispute that is pitting right- and left-leaning sites against their political allies: 

Surging spending on online ads has spawned a new generation of campaign consultants, skilled in new targeting tools and less inclined to spend money on Web sites merely because they support a partisan message. They are increasingly mimicking the tactics of commercial advertisers, which often aim ads not at particular sites but at certain kinds of users and whatever they happen to reading at the time.

 Advertising executives from the conservative Daily Caller and the liberal Prospect said the campaigns were put at a disadvantage by Google in particular. 

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