One of Mitt Romney’s top campaign advisers lashed out at President Obama’s reelection campaign for what he called “ugly distortions and lies” that he said were tarring the office of the presidency.

Eric Fehrnstrom seized on a television advertisement released this week by the pro-Obama super PAC Priorities USA that suggests Romney is at fault for the death of a woman whose husband lost his job after Bain Capital took over his steel mill.

Briefing reporters at Romney campaign headquarters, Fehrnstrom said that though a super PAC released it, he held the Obama campaign responsible for the ad, which independent fact checkers have called irresponsible and over-the-top.

“I don’t think a world champion limbo dancer could get any lower than the Obama campaign right now,” Fehrnstrom said. “In the process, Obama has squandered what has always been one of his key attributes — that he was a different kind of politician who was going to take us to a better place.”

Fehrnstrom said the Obama campaign has “gone from what started out as petty distortions and untruths to unbelievable exaggerations that diminish the office of the president and insult the American people.”

The ad features Joe Soptic, who was laid off from a Kansas City, Mo., steel plant that in 1993 was taken over by Romney’s investment firm, Bain Capital. Soptic says in the ad that he lost his health insurance during the takeover and shortly afterward his wife died of cancer.

In its response, the Obama campaign accused Romney of his own negative advertising.

“The Romney campaign’s faux outrage over an ad run by an outside group separate from our campaign rings extremely hollow,” Obama campaign spokeswoman Lis Smith said.

“Mitt Romney won the Republican primary only by tearing down each of his opponents with ruthlessly negative campaigning, including ads funded by outside allies. His campaign has questioned whether the President understands what it is to be American, attacked his patriotism, and is currently running an ad that a former president and authors of the welfare-to-work legislation have called a flat-out lie. When the Romney campaign finally reaches the high ground, we look forward to greeting them there.”

The president’s campaign aides have previously distanced themselves from the Soptic ad, strongly denying responsibility and noting that it does not control the ads and messages of Priorities USA.

But Soptic has worked with the Obama campaign to level attacks on Romney’s tenure at Bain. A few months ago he appeared as a surrogate on a conference call with reporters.

“This was a case where the Obama campaign has engaged not only in outright falsehood by accusing Mitt Romney of responsibility with the death of a woman, but beyond that, their campaign has deceived the public over what they knew about it,” Fehrnstrom said. “When you start running ads accusing your opponent of killing people, then you have lost credibility, and I think that’s where the Obama campaign finds itself today.”

A spate of national polls suggest the Obama campaign’s summer advertising onslaught against Romney may be working. But a second senior Romney adviser downplayed polls from CNN, Fox News and Reuters showing Obama widening a lead over Romney.

At the news briefing, the adviser argued that the polls were flukes in part because there had not been any major precipitating event in the campaign this summer that would result in such a shift. The adviser, who spoke on the condition of anonymity, added that new polls in the next 48 hours could paint a different picture.

“Guys, it’s the middle of summer, it’s the doldrums, it’s the middle of the Olympics,” the adviser told reporters. “There has not been any national news that would push these numbers from minus three to minus nine points. That’s a huge shift. You have to have some kind of precipitating event to move numbers like that.”

The adviser added that Rasmussen and Gallup polling has not shown such slippage and cautioned reporters against reading too much into any single poll. “If there was a sea change,” he said, “you’d know it.”

The Obama campaign, meanwhile, is accusing the Romney campaign of its own distortions with a television advertisement that asserts that Obama would “gut welfare reform by dropping work requirements.” A new Obama ad released Friday, titled “Blatant,” says Romney’s claims about welfare are not true.

Pressed by reporters about whether the Romney campaign is just as negative as the Obama campaign’s, Fehrnstrom said Obama’s attacks are “personal” while Romney’s are over a policy matter. Although he said the Romney campaign would “respond forcefully to Obama’s ugly distortions and lies,” Fehrnstrom pledged to take the “high ground.”

On a four-state bus tour beginning Saturday, Romney plans to talk about his plans to boost the economy, repeal Obama’s health-care overhaul and toughen policies with China. Fehrnstrom said Romney will highlight small businesses throughout his tour, which takes him through the battleground states of Virginia, North Carolina, Florida and Ohio.

“We are betting that a substantive campaign conducted on the high ground and focused primarily on jobs and the economy will trump a campaign that is designed to appeal to our worse instincts,” Fehrnstrom said.