Mitt Romney's campaign accused President Barack Obama's re-election team on Friday of "unbelievable distortions," citing an online ad from a pro-Obama group in which a former steel worker seems to link Romney to the death of his wife.
"I don't think a world champion limbo dancer could get any lower than the Obama campaign right now," said Eric Ferhnstrom, a senior adviser to Romney.
The focus of his complaints was an ad released this week by Priorities USA, a pro-Obama "Super PAC," or political action committee. The minute-long ad features Joe Soptic, who lost his job at a Kansas City steel plant after Bain Capital - the private equity firm Romney founded - took over the plant in 1993.
Less than a decade later, the plant was closed. Mr. Soptic and hundreds of others lost their jobs and health insurance.
"When Mitt Romney and Bain closed the plant, I lost my health care, and my family lost their health care," Mr. Soptic says in the ad. "A short time after that, my wife became ill. ... She passed away in 22 days."
The ad fits the Obama team's narrative that Governor Romney was a job-killing executive with little regard for the middle class. But Republicans cast the provocative linkage of Mr. Romney's actions to a woman's death as a new low in tactics for this campaign.
It also showed that although Super PACs operate independently from the candidates they support, their actions - particularly in promoting attack ads - can create some difficult moments for those candidates.
President Obama's team has tried to distance itself from the ad involving Soptic - whom the campaign had featured in a conference call in May. It notes that while employing former Obama aides, Priorities USA operates separately from the campaign.
White House spokesman Jay Carney questioned the sincerity of Republicans' outrage over the Soptic ad on Friday and pointed to a Republican PAC that continues to run ads suggesting President Obama is not a U.S. citizen and therefore is ineligible to be president.
"I am not aware of the new Super PAC ad that you reference," Mr. Carney told a reporter at a White House briefing, while questioning whether Republicans were willing to denounce a "Republican Super PAC ad that questions whether or not the president is an American citizen."
Political analysts said that although much of the wrangling between the Obama and Romney teams was typical for a presidential campaign, the level of the attacks appeared to be something of a benchmark.
"We have seen an acceleration in recent election cycles of how far campaigns are willing to go," said Julian Zelizer, a history professor at Princeton University. "While taking quotes out of context and unfair charges against a candidate have been standard in elections for many years, now the campaigns seem to be veering into outright deception."
As it prepared on Friday to launch a four-day bus tour of the key states of Virginia, North Carolina, Florida and Ohio, Romney's campaign was withering in its criticism of Obama.
Professor Fehrnstrom, briefing reporters at Romney's headquarters in Boston, noted that an Obama operative previously had suggested that Romney had broken the law by taking advantage of tax loopholes.
And "when you start running ads accusing your opponent of killing people," he said, "then you have lost your credibility."
The Romney campaign also put out an ad, called "America Deserves Better," that blasted Obama for trying "to use the tragedy of a woman's death for political gain."
Mr. Romney's bus tour comes at a time when polls are indicating that attacks on Mr. Romney by Mr. Obama and groups that support him could be working, and that what has been a slight Obama lead could be growing.
A Reuters/Ipsos poll this week indicated that President Obama held a 7-point lead over Romney, up 1 point from last month, even though less than one-third of those surveyed thought the United States was on the right track.
A CNN poll also put Mr. Obama's advantage at 7 points, while a Fox News poll gave the president a 9-point advantage.
Republicans are hoping Governor Romney might get a bounce by picking a vice presidential running mate, an announcement that could come soon.
Mr. Romney's short list appears to include former Minnesota governor Tim Pawlenty, Ohio Senator Rob Portman and Wisconsin Congressman Paul Ryan.
On the bus tour, the former Massachusetts governor will appear with Portman in Ohio, Senator Marco Rubio in Florida and Governor Bob McDonnell in Virginia.
A top Romney adviser on Friday rejected the notion that Obama's lead is growing.
At a time when many Americans are taking summer vacations, the adviser said, "people are not paying as much attention to this process as we think they are."