Steve Rattner: Mitt Romney Used 'Every Trick In The Book' To Avoid Tax Penalties (VIDEO)

WASHINGTON -- Steve Rattner, President Barack Obama's former car czar, weighed in on Mitt Romney's tax returns Sunday, arguing that the presumptive Republican nominee took advantage of an especially large number of loopholes.

"If you say to your tax people, as he seems to have done, 'I want every trick in the book. I want to push this to the edge,'" Rattner said during an appearance on "Fareed Zakaria GPS" on CNN. "I will tell you that as a private equity guy, I'm familiar with many of the things that he did. And I know many people who have done many of the things that he did. I do not know anyone who did everything that he did."

"Some of what he did, like the IRA, I have asked fellow private equity guys," Rattner said, referencing the account in which Romney has stored up to $100 million tax-free. "None of us had even known this was a possible trick, if you will. He has pushed the envelope all the way to the edge, to his benefit, and I think that Americans would find that pretty distasteful."

Romney has declined to release multiple years' worth of tax returns, disclosing only those from 2010 and estimates from 2011. Rattner called Romney overly secretive Sunday, speculating that he was attempting to hide more instances of using innovative and questionable accounting tricks.

Rattner, who hails from the world of private equity, has occasionally served as a voice of sympathy for Romney as his business career has come under heavy attack. His comments, then, carry a bit more weight than the average criticism from an Obama ally.