TITLE: "It Won't"

LENGTH: 30 seconds

AIRING: Pennsylvania

SCRIPT: Obama: "I'm Barack Obama, and I approved this message."

Sen. Bob Casey, D-Pa.: "In towns like yours and mine, families are struggling with bills they can't afford and jobs moving away. It has to change but it won't until we change Washington. That's why I believe in Barack Obama. I've worked with him. I've seen him stand up to the lobbyists and special interests. And like us, he's tired of the political games and division that stops anything from getting done. Barack Obama knows Pennsylvania's hurting. He can unite America and bring real change."

KEY IMAGES: Casey, dressed in casual clothes, talks as he walks toward the camera in a town labeled as Scranton. Obama is shown in two still photos wearing a business suit, and in videos wearing an open-collar shirt, with his sleeves rolled up, as he talks and strolls with voters and a construction worker.

ANALYSIS: Casey, a freshman senator, is a key endorser of Obama in a state whose governor and big-city mayors are backing Sen. Hillary Rodham Clinton. Like his late father, a well-liked governor, Casey opposes abortion rights and is popular among many Catholics and blue-collar Democrats who are crucial to Clinton's hopes.

Without mentioning Clinton, the ad hints at Obama's claims that she is part of a tiresome, divisive and ineffective Washington power structure. It addresses working class families who are "hurting" at a time when Obama is being criticized for saying in a private meeting that many economically distressed Pennsylvanians "cling to" guns, religion and a dislike of outsiders because they are bitter.

Scranton, located in a region hit hard by job losses, is a battleground where Obama would like to limit Clinton's appeal. Her father grew up in Scranton and the family vacationed there often, as Clinton always reminds Pennsylvania voters.

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Analysis by Associated Press writer Charles Babington