"If you watch me on the campaign trail ... I'm talking about how we put Americans back to work. and there are sharp differences between myself and [presumed GOP presidential nominee Mitt] Romney in terms of how we would do that," Obama told reporters at an impromptu White House news conference.
"Now, if you look at the overall trajectory of our campaign and the ads that I've approved and are produced by my campaign, you'll see that we point out sharp differences between the candidates, but we don't go out of bounds."
Obama said Romney has been running false ads on welfare and repeating those falsehoods on the campaign trail.
"You've got Governor Romney creating as a centerpiece of his campaign this notion that we're taking the work requirement out of welfare, which every single person here who's looked at it says is patently false," Obama said. "What he's arguing is somehow we have changed the welfare requirement -- the work requirement in our welfare laws. And, in fact, what's happened was that my administration, responding to the requests of five governors, including two Republican governors, agreed to approve giving them, those states, some flexibility in how they manage their welfare rolls as long as it produced 20 percent increases in the number of people who are getting work. ...
"Everybody who has looked at this says what Governor Romney is saying is absolutely wrong. Not only are his super PACs running millions of dollars' worth of ads making this claim; Governor Romney himself is approving this and saying it on the stump."
In contrast, Obama said the ad put together by a PAC supporting him that linked Romney to the death of the wife of a man who lost his job when Romney's Bain Capital bought a company "has barely run. I think it ran once" and "I don't think that Governor Romney is somehow responsible for the death of the woman that was portrayed in that ad."