Obama Campaign Ad Speculates Mitt Romney Might Have Paid Nothing In Taxes

A new ad released by the Obama campaign Thursday suggests that Mitt Romney might have paid nothing in taxes at some point. The ad plays a clip of a recent interview in which Romney said he was "happy to go back and look" to see if he had paid a rate lower than 13.9 percent -- but he never did get back to the voters on that.

"Did Romney pay 10 percent in taxes? 5 percent? Zero?" asks a narrator. "We don’t know."

The campaign says the ad is "following" Romney through Virginia, North Carolina, Florida and Ohio next week.