Updated

TITLE: "Son of Boss"

LENGTH: 30 seconds.

AIRING: Florida, Ohio, North Carolina and Virginia — the four states Romney will visit on his bus tour starting Saturday.

KEY IMAGES: Mitt Romney, in a recent interview with ABC News, is asked whether he ever paid less than 13.9 percent in taxes.

"I haven't calculated that. I'm happy to go back and look," Romney says.

Shadows, grainy horizontal lines and color desaturation obscure the original video footage.

"Did Romney pay 10 percent in taxes? Five percent? Zero? We don't know," says a narrator. "But we do know that Romney personally approved over $70 million in fictional losses to the IRS as part of the notorious 'Son of Boss' tax scandal — one of the largest tax avoidance schemes in history."

The ad closes on a faded, blue-tinted image of Romney, with white words superimposed that mimic the narrator: "Isn't it time for Romney to come clean?"

ANALYSIS: Obama's campaign was elated late last month when Senate Majority Leader Harry Reid, D-Nev., suggested that Romney hadn't paid any taxes for 10 years, citing an unnamed investor in Romney's former company. But with no evidence to back it up, the Obama campaign treaded carefully. The White House said Reid was speaking for himself, and top campaign adviser Robert Gibbs took to CNN to say that nobody controls Reid.

Obama's new ad marks the first time his campaign has, in its own words, raised the idea that Romney may have paid no taxes — a claim that Romney has rejected but declined to back up by releasing more than a year's worth of tax returns.

The new ad is part and parcel to Obama's strategy to paint his opponent as a wealthy plutocrat more concerned about his own prosperity than that of the nation.

The campaign also wants to cast a shadow over Romney's integrity and commitment to transparency. By using dark, grainy shots of Romney, the ad insinuates that Romney has something to hide.

The second half of the ad deploys a new line of attack, referencing media reports about a tax shelter pursued by Marriott International Inc. while Romney served on the company's board. In doing so, Obama's campaign extends a narrative about Romney being out of touch with how the economy affects regular people. It's the same theme his campaign is hitting when it reminds voters about Romney's Swiss bank account or his business interests in Bermuda and the Cayman Islands.

The Romney campaign dismisses the new ad as "another dishonorable and dishonest attack."

Obama has repeatedly reminded voters that it was Romney, not Democrats, who decided to make his business resume the centerpiece of his argument for why he's better equipped to grow the economy. The Obama campaign hopes that when voters take a closer look at Romney's business record, instead of a model for success, they'll see an example of rich people playing by different rules than everyone else.