Mitt Romney gave voters a "cow pie of distortion" when he talked about the national debt, President Obama told supporters in Iowa on Thursday night.

It was part of a harsh critique Obama gave of his GOP rival's economic credentials. Obama again slammed Romney's tenure at Bain Capital and reminded voters that the former Massachusetts governor once called corporations "people."

"I know Gov. Romney came to Des Moines last week; warned about a 'prairie fire of debt.' That’s what he said. But he left out some facts. His speech was more like a cow pie of distortion. I don’t know whose record he twisted the most — mine or his," Obama told the crowd.

He noted of Romney: "He and his folks, they’ve got the nerve to go around saying they're somehow going to bring down the deficit. Economists who have looked at his plan say it would swell our deficits by trillions of dollars."

Obama's appearance in Newton, Iowa, on Thursday followed Romney's stop in the critical swing state a few weeks ago, when the presumptive GOP nominee argued the country suffered from excess spending and too much debt.

"When the men and women who settled the Iowa prairie saw a fire in the distance, they didn’t look around for someone else to save them or go back to sleep hoping the wind might blow another direction. They knew that their survival was up to them," Romney said in his Des Moines speech. "A prairie fire of debt is sweeping across Iowa and our nation and every day we fail to act that fire gets closer to the homes and children we love."

Polls show voters rank the economy as the most important issue heading into November's election, and it's an issue both candidates talk about at length.

Obama, making his first campaign stop in Iowa since he officially announced his reelection bid, mentioned Romney repeatedly in his remarks, which he has done with increasing frequency on the campaign trail.

And his speech appeared tailored for blue-collar voters, a key constituency in the swing state, as he slammed private equity firms for their treatment of workers — a reference to Romney's time at Bain Capital.

"Workers get laid off. Benefits disappear. Pensions are cut. Factories go dark," he said, adding that "investors walk off with big returns, and working folks get stuck holding the bag."

Romney's campaign fired back.

“A president who broke his promise to cut the deficit in half by the end of his first term has no standing when it comes to fiscal responsibility," said Romney spokesman Ryan Williams. "When you listen to President Obama’s campaign speeches, it’s as if he's forgotten that he’s been president for nearly four years and has a record to defend. President Obama has proven beyond all doubt that he is not serious about fixing our country’s spending problem.”