The pro-Obama forces, however, are not letting go of Romney's comments about the "47 percent" of Americans who don't pay income taxes. A new ad by the pro-Obama super PAC Priorities USA Action uses footage from the leaked fundraiser video, in which Romney says Americans who don't pay income tax are "dependent upon the government" and "believe that they are victims." It also features an apparent image of the house where the now-famous event was held.

"Victims?" the narrator asks, before cutting to another image of a much more modest house, and then to a woman bathing a baby in the sink. "Behind these doors, middle-class families struggle. And Romney will make things even tougher, raising taxes by up to $2,000 to give multimillionaires a $250,000 tax break."

An Obama for America ad released Tuesday afternoon struck a similar note, featuring a mom who "would be stretched even more under Mitt Romney," according to the spot's narrator. "To fund his tax cuts for millionaires, Romney could take away middle class deductions for child care, home mortgages, and college tuition."

Meanwhile, the super PAC American Bridge has released a new web ad wondering if Romney is actually a member of the 47 percent, and reiterates calls him to "show us your tax returns."

Both of the pro-Obama television ads will play in eight key battleground states, cumulatively. The Romney campaign does not divulge information about its ad buys, but the pro-Romney Restore Our Future ad will air in Michigan and Wisconsin.