Romney accused Obama of waging a "war on coal" while the president mercilessly mocked his foe as oblivious to the benefits of wind power, as both candidates tapped a political seam that could be crucial in a tight election.
Obama built on an emerging theme that Romney, a wealthy former venture capitalist, simply does not understand the heartland economy, and the hard-won achievements of regular people, using wind power as a prism.
"If he knew what you've been doing, he'd know that about 20 percent of Iowa's electricity now comes from wind, powering our homes and factories and businesses in a way that's clean and renewable," Obama told a crowd in Iowa.
Obama's sleek black bus is spending three days rolling across the corn-filled prairies of Iowa, a battleground in the November 6 election, where clusters of towering white windmills are an increasingly common sight.
"Governor Romney even explained his energy policy this way... 'You can't drive a car with a windmill on it.'" Obama said.
"That's what he said about wind power."
"I don't know if he has actually tried that -- I know he has had other things on his car," Obama said, referring to a notorious story about how Romney once drove to Canada with his pet dog strapped in its kennel to the car roof.
Obama's campaign believes it can move votes in Iowa by highlighting Romney's opposition to an extension of a wind energy tax credit which expires this year.
"He's said new sources of energy like these are 'imaginary.' His running mate (Paul Ryan) calls them a 'fad," Obama told an 800 strong crowd, on an idyllic farm fringed by gently waving cornfields.
"I wonder if he actually tried that. That's something I would have liked to see," he added. "But if he really wants to learn something about wind energy, Iowa, all he has to do is pay attention to what you've been doing."
Obama says wind energy support 7,000 jobs in Iowa and 75,000 across the country, and styles his energy policies as both creating vitally needed green energy sources and creating jobs in the 21st Century economy.
Romney's campaign has said he would let the wind credit expire because he thinks government should not be in the business of supporting one industry over another.
As an example of what they see as the government weighting the energy market, Republicans highlight the fate of the solar energy firm Solyndra, which went bankrupt after getting a $500 million government loan guarantee.
Romney planned his own energy attack in a battleground state, in Ohio, blasting the president for new environmental regulations which he says have forced the closure of dozens of power plants.
His tactic was similar to Obama's, leveraging a key local debate to try to shift wavering voters on a key spot of the US electoral map. Ohio is considered a must-win for Romney if he is to capture the presidency.
"I see how he's been waging war on coal," Romney told supporters at the Century Mine in the village of Beallsville in the heart of eastern Ohio coal country, as rows of weary, soot-covered miners stood behind him as a backdrop.
The Obama administration says clean coal is part of the president's "all of the above" energy strategy, and it has funded research and development in low-emissions coal.
But Romney, as he often does on the campaign trail, mocked the president's energy plan, saying Obama "is for all the sources of energy that come from above the ground, none of those that come from below the ground, like oil and coal and gas."
Romney said the country must "take advantage of our energy resources -- our coal, our gas, our oil, our renewables, our nuclear.
"We have 250 years of coal; why in the heck wouldn't we use it?"
Romney, who on Tuesday wraps up his own four-day bus tour through battleground states, signed miners' helmets after his address.
