TWO days after President Obama’s first debate against Mitt Romney, Stephanie Cutter, a deputy campaign manager for the Obama re-election effort, decided to tweak Mr. Romney for his attack on federal funding for PBS. On Twitter, Ms. Cutter, known for her dry sense of humor and sharp edge, circulated a photo of Big Bird outside an Obama rally with the hashtag #ProtectSesameStreetNotWallStreet to her 42,700-plus followers. The Big Bird attacks started to take on a life of their own. The following week, the Obama campaign introduced a tongue-in-cheek ad that compares Big Bird to Bernard L. Madoff and other corporate...