Mitt Romney lashed Barack Obama as "angry and desperate" and told him to take his "hate" home to Chicago in an outburst which prompted the president's camp to brand him "unhinged."
A sudden and bitter escalation to the White House race was triggered when Vice President Joe Biden said in the one-time slave state of Virginia that Romney's plans to slash banking regulation would "put y'all back in chains."
A furious Romney fired back at a rally in Ohio, accusing Obama, who ran in 2008 vowing to heal political divides, of trying to "smash America apart" to cobble together a 51 percent majority to win a second term.
"This is what an angry and desperate presidency looks like," he said, in the most charged exchanges of the campaign so far.
"Mr President, take your campaign of division and anger and hate back to Chicago and let us get about rebuilding and reuniting America," the Republican candidate said.
Democrat Obama, in his final event of the day, under a setting sun in Waterloo, Iowa, decided to stay above the fray, and left it to his campaign to use the outburst to implicitly question his foe's temperament to lead.
"Governor Romney's comments tonight seemed unhinged and particularly strange coming at a time when he's pouring tens of millions of dollars into negative ads that are demonstrably false," Obama spokesman Ben LaBolt said.
Rising temperatures between the campaigns came as Romney and Obama trekked across crucial electoral territory in dueling bus tours as both geared up for their nominating conventions and a race to the finish on November 6.
Obama thrust home his claim that Romney, a multi-millionaire former venture capitalist would further enrich his wealthy friends with tax cuts -- and put the burden on a middle class struggling to cope in a slow economic recovery.
Romney paints Obama as out of ideas, an enemy of job creating small businesses and bent on a big government takeover of many aspects of American life and questions whether he really understands his home country.
Republicans said Tuesday that emerging party favorite, Chris Christie, the sharp-tongued governor of New Jersey, will deliver the keynote address at their nominating convention in Tampa, Florida, between August 27 and 30.
Such appearances can catapult politicians to national prominence: Obama's electrifying address at the Democratic convention in 2004 launched his meteoric rise to the presidency.
Both Romney and Obama Tuesday settled on the politically charged issue of energy sources, past and present, as the latest prism for their differences.
Romney, drawing big crowds in coal country in Ohio, a key swing state, accused Obama of waging a "war on coal" by hampering America's mining industry with environmental emissions regulations.
Flanked by miners, Romney mocked the president's energy plan, saying he was opposed to "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."
Obama, barnstorming across Iowa, another tightly contested battleground, sarcastically charged that Romney simply did not understand the heartland economy, as he attack the Republican over wind power.
"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.
"Governor Romney even explained his energy policy this way... 'You can't drive a car with a windmill on it.'" Obama said.
"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.
To drive home his point the president stopped his sleek black bus at a family farm, where 52 huge turbines harness enough wind to power thousands of Iowa homes.
Obama says wind energy supports 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.
The fury of Tuesday's campaigning pushed Romney's newly minted vice presidential nominee Paul Ryan, a favorite of the party's conservative base, into the background, though there were signs of a quickening media vetting operation into the 42-year-old Wisconsin lawmaker's past and policies.