Obama's campaign has refused to ask the group, Priorities USA Action, to pull the spot and one of its co-founders has defended the ad.
"I don't know what happened to a campaign of hope and change. I thought he was a new kind of politician," Romney said, alluding to Obama's previous campaign slogan, during an interview on Bill Bennett's radio program, "Morning in America."
The ad features a man whose wife died of cancer after he was laid off and they both lost their health insurance. Joe Soptic lost his job after the company he worked for was bought by the private equity firm Romney once ran.
"I do not think Mitt Romney realizes what he's done to anyone, and furthermore I do not think Mitt Romney is concerned," Soptic says in the ad.
Romney didn't mention the ad in remarks at a Park Avenue fundraiser Thursday morning in New York City. "I need you to speak the truth -- talk to your friends and colleagues," he implored donors at a breakfast that raised more than $1.5 million for his campaign.
Woody Johnson, a top fundraiser, told the crowd the campaign is "halfway" to its ultimate fundraising goals for the election.
Romney campaign spokeswoman Andrea Saul said it was "despicable" for the ad to link Romney to the woman's death.
In the radio interview, Romney said Obama's campaign ad "just keep on running," even though various fact-checking organizations have challenged their accuracy.
Romney charged that his opponent's campaign has "focused almost exclusively on personal attacks" when it should be talking about how to resuscitate the struggling economy and create jobs.
At the same time, Romney's team rolled out an ad saying Obama has declared "war on religion." It cited new health rules mandating insurance coverage for birth control without co-pays, which the ad says forces religious institutions to "go against their faith." Obama says exemptions for churches and compromise language on charities fully protects religious freedom.
Later Thursday, Obama was to rally supporters in Pueblo and Colorado Springs on the second day of a two-day campaign swing through Colorado. On Wednesday, he made a pitch to female voters in Denver and reached out to Republican-leaning Grand Junction.
Obama carried Colorado in 2008, but he and Romney are engaged in a tight contest for the state's nine electoral votes.
Romney had no public events Thursday. He was raising money in New York, and preparing for Friday's start of a four-state bus trip 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 to extend tax cuts without adding to the deficit or forcing moderate-income people 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 that Romney's 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."
Saul, Romney's spokeswoman, drew criticism from some conservatives when, in criticizing the Priorities USA Action ad, she cited the health care law Romney put in place in Massachusetts when he was governor.
"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 requires people to buy health coverage. That requirement is similar to the provision in the federal law enacted by Obama, which conservatives despite and Romney has vowed to repeal.
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