Mitt Romney’s visit to the Iowa State Fair on Thursday might have been the best debate prep session he could have hoped for.

Romney’s appearance at the fair’s soapbox grew unusually testy when a few angry people heckled the Republican presidential candidate over his declaration not to raise taxes. They urged the campaign front-runner to increase taxes on the wealthy to help fund such entitlement programs as Social Security and Medicare.

Romney explained that one way to fulfill promises on entitlement programs is to “raise taxes on people,” but before he could articulate his position on not raising taxes, someone interrupted.

“Corporations!” a protester shouted, apparently urging Romney to raise taxes on corporations that have benefited from loopholes in the tax code. “Corporations!”

“Corporations are people, my friend,” Romney said.

Some people in the front of the audience shouted, “No, they’re not!”

“Of course they are,” Romney said. “Everything corporations earn ultimately goes to people. Where do you think it goes?”

The heated exchange prompted an attack from Democratic National Committee Chairwoman Debbie Wasserman Schultz.

“Mitt Romney’s comment today that ‘corporations are people’ is one more indication that Romney and the Republicans on the campaign trail and in Washington have misplaced priorities,” she said in a statement, calling the comment a “shocking admission.”

There were other tense moments in Romney’s 20-minute appearance at the fair. People interrupted the former Massachusetts governor with chants of “Wall Street greed!” Some in the audience tried to shout questions over Romney, and he at times shouted back.

“Hold on a moment, let me speak! Hold on a moment!” he said.

“You get to ask your question, I get to give my answer and if you don’t like my answer you can vote for someone else,” Romney said.

At one point, Romney poked fun at the hecklers, saying: “My guess is they won’t be voting for me.”

The hecklers were far outnumbered by Romney supporters, nearly 300 in all, who cheered over the heckling. For Romney, the exchange was a rare unscripted and impassioned moment that his advisers said helped him demonstrate to voters that he has the stomach to fight.

Romney was the first of several candidates scheduled to speak at the Des Moines Register soapbox this week. He stood in a short-sleeved shirt and casual pants, his left leg propped on a bale of hay, and delivered a stump speech that was more fiery than typical.

“The nation as a whole is really struggling,” Romney said. “And part of that reason is we’re led by a man who’s a fine fella, but he’s out of his depth and doesn’t understand how the economy works.”

Romney argued that he does, given his 25 years of private sector experience.

“Sometimes I wonder whether [Obama] takes his political inspiration from the social Democrats of Europe,” Romney said. “I don’t think Europe is working there. I sure don’t think Europe will work here. I happen to believe that we got it right and they got it wrong. I believe in freedom and opportunity, American-style.”