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 criminals. “Big, yellow, a menace to our economy,” the ominous voice-over intoned.

It was a typical quick-response effort by Ms. Cutter, doing damage control after an admittedly lackluster performance by the president. “She spotted right away that this was something that was trending out there and that was making an impact,” David Axelrod, the president’s chief strategist, said of Ms. Cutter, who was not involved in the making of the ad itself.

Ms. Cutter, who turns 44 on Oct. 22, has emerged as Mr. Obama’s one-woman attack squad. In the process, she has become a popular but polarizing face of a campaign that until recently had been largely dominated by middle-aged white men.