WASHINGTON —  Mitt Romney’s campaign fiercely protested a searing attack ad aired by allies of President Barack Obama on Wednesday, but drew expressions of dismay from conservatives when an aide to the former Massachusetts governor invoked the benefits of a state health care system he signed into law.

“If people had been in Massachusetts under Gov. Romney’s health care plan, they would have had health care,” spokeswoman Andrea Saul said in an interview on Fox News. The Republican presidential candidate 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 he has vowed to repeal.

Saul volunteered her observation after sharply denouncing the ad. In it, which a grim-faced former steelworker, Joe Soptic, suggests that Romney and Bain Capital, the private equity firm he founded, might bear some responsibility for his wife’s death from cancer several years ago.

“It’s just despicable, to be honest,” Saul said of the commercial, which is aired by Priorities USA Action, a super PAC that supports Obama’s re-election. “Of course he doesn’t want to see ill come to anyone.”

Independent fact checkers judged the commercial harshly, sometimes unusually so.

Additionally, the Romney’s campaign alleged that the president’s campaign “lied repeatedly about its knowledge of the content” of the commercial. The allegations were denied.

Whatever the particulars, conservatives were quick to react to Saul’s remark about the health care law that Romney signed as governor of Massachusetts.

Conservative talk show host Rush Limbaugh excoriated Democrats over the TV spot. But he added that the Romney aide’s remarks were “a potential gold mine for the Obamaites, because they can say, ‘Well, yeah, and Romneycare’s the foundation for our plan, Obamacare,’ which they are already out there saying.”

The back and forth over the commercial largely overshadowed the day’s campaign activities by the president and his challenger.

Romney campaigned in Iowa, where he drew a standing ovation for promising to repeal “Obamacare,” the derisive label that Republicans long ago hung on the law the president won from Congress.

“That doesn’t mean that health care is perfect,” he said. “We’ve got to some reforms in health care. And I have some experiences doing that, as you know.”

Obama was in Colorado, where he embraced the Obamacare tag in an appearance before an audience largely made up of women.

“I actually like the name because I do care,” he said. “That’s why we fought so hard to make it happen.”

The president’s campaign aides said throughout the day they had no connection with the controversial television commercial and added that they didn’t know the specifics of when Soptic’s wife became ill. Republicans responded quickly with evidence of a conference call arranged last spring by Stephanie Cutter, a top aide in Obama’s campaign, in which reporters were given an opportunity to speak with Soptic.

Under federal law, the president’s campaign may not coordinate its activities with independent groups such as Priorities USA Action.

Privately, some Republican strategists expressed chagrin at the favorable reference to the Massachusetts law that Romney signed. One prominent conservative blogger, Erick Erickson of Redstate.com, wrote forebodingly that the episode “may mark the day the Romney campaign died.”

That seemed unlikely in the extreme.

Polls make the race a close one, to be decided in a battle for eight or so swing states where neither candidate has a decided edge. Key campaign events are yet to unfold, including national political conventions set to begin later this month, Romney’s selection of a vice presidential running mate, and a spate of campaign debates a few weeks before the election.

Romney has been outraising Obama in the competition for campaign cash in the past three months, and is backed by deep-pocketed super PACS that have vowed to spend heavily to help him win the White House.

Ironically, given the events of the day, Democratic outside groups have generally struggled to keep pace with those aligned with Romney.

Bill Burton, a former White House aide and co-founder of Priorities USA Action, did not respond to a request for comments about the ad that his group is airing.

The ad “tells the story of one guy,” Burton said. “Joe Soptic was fired” after Bain Capital took control of the company “and as a result when his wife got sick they had no insurance.”

In the ad, Soptic says that the plant where he worked was closed by Romney and Bain in 2001. “I lost my health care, and my family lost their health care. And a short time after that my wife became ill. I don’t know how long she was sick and I think maybe she didn’t say anything because she knew that we couldn’t afford the insurance.”

By the time she went to the hospital, he added, she was found to have cancer and died 22 days later.

“I do not think Mitt Romney realizes what he’s done to anyone,” Soptic says, “and furthermore I do not think Mitt Romney is concerned.”

Romney has long said he left Bain Capital in 1999 to take over the management of the troubled 2002 Salt Lake Olympics Games.

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Associated Press writers Steve Peoples in Iowa, Julie Pace in Colorado, Kasie Hunt in New York and Matthew Daly in Washington contributed to this report.