Mitt Romney's campaign unloaded on President Obama during a conference call with reporters Tuesday, with top surrogate John Sununu blasting the president as coming from a "felon environment" in Chicago and suggesting the president should "learn how to be an American."

The former New Hampshire governor walked back the later comment by the end of the call — clarifying that "the president has to learn the American formula for creating business" — but the moment was indicative of a series of shots at the president's campaign.

Clearly believing the best defense was a good offense, the Romney campaign looked to battle back against persistent questions on their candidate's tenure at Bain Capital by painting the president as the product of notorious corruption in local Chicago politics.

It's a line of attack Team Romney began this week and, when questioned on it, argued that the president's political donors and supporters received preferential access to the administration and government contracts.

"It ties back completely to where President Obama comes from. He comes out of that murky political world in Chicago where 'politician' and 'felon' have become synonymous," Sununu said. "It is an area where two of their governors are in prison, it is an area where Tony Rezko is a convicted felon and in prison and just happened to be the guy who did a smarmy real estate deal with the president."

In citing Rezko, a Chicago-area political operative who was convicted of demanding kickbacks from Illinois businesses to do business with the state, the Romney campaign signaled a new willingness to get into the mud. Obama has had to answer questions about his ties to Rezko, and it was a major issue in the 2008 campaign.

"I am shocked the president introduced the word 'felon' into the political discourse. ... If you introduce the word felon into the political discourse, you open yourself up again to the discussion of his Chicago roots and the Chicago political/felon environment that he came from," Sununu said.

At other points in the call, small-business owners who supported Romney referred to the president's economic policies as "socialism" and mocked the president for using a teleprompter.

The Obama campaign said Tuesday that Sununu's comments amounted to a "meltdown."

“The Romney campaign has officially gone off the deep end," spokeswoman Lis Smith said. "The question is what else they’ll pull to avoid answering serious questions about Romney’s tenure at Bain Capital and investments in foreign tax havens and offshore accounts This meltdown and over-the-top rhetoric won’t make things better- it only calls attention to how desperate they are to change the conversation.”