Romney goes on to describe the president as "an old school liberal whose first instinct is to see free enterprise as the villain and government as the hero."

There have long been whispers of discontent between the last two Democratic presidents, with suggestion that Clinton does not approve of Obama's job as president and remains frustrated that his wife, Hillary, did not emerge from the 2008 presidential primary. But Clinton has lent his hand to the Obama reelection effort, cutting an ad praising the president's decision to authorize the Osama bin Laden raid and appearing at fundraisers on his behalf.

Earlier Tuesday, Clinton spoke at the Peter G. Peterson Foundation's 2012 Fiscal Summit in Washington and suggested Obama be more aggressive in pushing deficit reduction when facing off against Romney.

"The president, I think, should talk more about the Medicare savings he has proposed, and the defense cuts he has proposed, and the fact that he proposes, and this – I disagree with this, by the way – he proposes to take discretionary non-defense spending to its lowest percentage of GDP since president Eisenhower was in office,” Clinton said. “We ought to be talking about this stuff. He has at least tried to honor the deal he made with the Republicans, and I think he should talk more about it, and I think they should talk more about it."