Romney campaign spokeswoman Andrea Saul labeled the ad linking Romney to a woman's death from cancer "despicable," but the Obama campaign refused to call on Priorities USA Action to pull the TV spot. Bill Burton, a former White House aide and co-founder of the group, defended the ad.
In the ad, a steelworker suggests that Romney and the private equity firm he founded might bear some responsibility for his wife's death from cancer because the firm closed the plant and he lost his health insurance.
Romney charged Thursday that the ads being run on Obama's behalf have crossed the boundaries of appropriate campaign rhetoric.
In an interview broadcast on Bill Bennett's "Morning in America" radio show, the former Massachusetts governor said the Obama campaign commercials "just keep on running," even though various fact-checking organizations have challenged their accuracy.
Without making any direct reference to the ad about the woman who died from cancer, Romney told Bennett, "I don't know what happened to a campaign of hope and change. I thought he was a new kind of politician."
Romney charged that the Obama campaign has "focused almost exclusively on personal attacks" when it should be talking about how to resuscitate the struggling economy and create jobs.
Obama later Thursday was to rally supporters in Pueblo and Colorado Springs after making a pitch to female voters in Denver and reaching out to Republican-leaning Grand Junction. He carried Colorado in 2008, but he and Romney are engaged in a tight contest for the state's nine electoral votes.
Romney was raising money in New York as his campaign prepares for a bus trip through battleground states and a decision on a running mate.
In Colorado, Obama is trying to undermine Romney's arguments that Obama has failed to revitalize the economy nearly four years after the economic downturn. The president told voters in Grand Junction that Romney is struggling to explain how proposed tax cuts could continue without adding to the deficit or forcing Americans with moderate incomes to pay more.
"There was a whole different kind of gymnastics being performed by Mr. Romney than what's been happening in the Olympics," Obama said. He accused his opponent of "twisting" and "turning" and "doing backflips" over a report by a think tank that found his tax plan could force middle-class workers to lose tax breaks and pay more.
A new Quinnipiac University poll shows Obama and Romney tied among voters in Colorado households earning between $30,000 and $50,000 per year -- an important target. Obama leads among voters with lower incomes while Romney is favored by those making more.
Romney campaigned Wednesday in Iowa, where he drew a standing ovation for promising to repeal "Obamacare," the label Republicans have used to deride Obama's health care law.
"That doesn't mean that health care is perfect," Romney said. "We've got to do some reforms in health care. And I have some experiences doing that, as you know."
Obama, campaigning in Denver before an audience largely made up of women, said he liked the "Obamacare" tag.
"I actually like the name because I do care," he said. "That's why we fought so hard to make it happen."
Romney's spokeswoman drew expressions of dismay from some conservatives when she cited Romney's own health care law from his days as governor of Massachusetts in criticizing the steelworker ad.
"If people had been in Massachusetts under Gov. Romney's health care plan, they would have had health care," Saul said in an interview on Fox News. Romney himself rarely mentions the law, which contains a requirement to purchase health coverage similar to the one in the federal law that conservatives despise and Romney has vowed to repeal.