Mitt Romney is adamant: "I will press for full repeal of 'Obamacare,' which will save hundreds of billions of dollars." But the nonpartisan Congressional Budget Office ? whose data the campaign has cited as the source of its assertion ? says that the 2010 federal healthcare law should cut deficits $210 billion from 2012 to 2021. The bottom line: "It's actually not known who's right," said Amitabh Chandra, economist and professor of public policy at Harvard University."If the law goes through as it is, it will save us money," he said. But what if Washington lawmakers ? as they often do ? balk at implementing some of the cost-savings features, such as higher taxes or dramatic cuts in Medicare? There go the big savings. "Congress has a history of doing things like that," Chandra said. The quandary over deciding who's right is typical when trying to evaluate campaign assertions. It's difficult to say whether Romney is accurate or exaggerating, although some analysts said that, at the least, he's using CBO's analysis selectively. The agency is widely regarded as Capitol Hill's leading independent authority on the fiscal impact of legislation, and its reviews can only deal with current law.