Thanks to social media, the remark quickly escalated into a fracas over the role of women in American society.
It gave Mitt Romney, the likely Republican nominee for president who is scrambling to improve his ratings among women voters, a chance to reach out to them through his wife. And it sent Democratic President Obama's top campaign staff members - and by Thursday afternoon, the president and first lady - rushing to disavow the pundit's remark.
Rosen, a Democratic pundit who has advised the Democratic National Committee, said during an interview on CNN that she tried to make the point that Ann Romney, as the wife of a wealthy private equity executive, does not understand many of the economic challenges faced by typical Americans.
But she slipped by saying that Mrs. Romney had "never worked a day in her life."
Mitt Romney's campaign - which saw his ratings among women take a dive as Republican presidential candidates sparred over abortion, contraception and other divisive social issues - seized the moment.
Ann Romney launched her own Twitter account after Rosen's interview, and she used her first-ever tweet to say: "I made a choice to stay home and raise five boys. Believe me, it was hard work."
That set off alarms among Democrats, who are keen to hold on to Obama's current advantage among women in a Nov. 6 election in which women voters could tip the balance.
"I could not disagree with Hilary Rosen any more strongly. Her comments were wrong and family should be off limits. She should apologize," Obama campaign director Jim Messina tweeted, shortly after Rosen spoke.
David Axelrod, a top adviser to Obama's campaign, also weighed in quickly on Twitter, calling Rosen's comments "inappropriate and offensive."
The president spoke up Thursday afternoon, telling an Iowa television station that "there's no tougher job than being a mom.
"I don't have a lot of patience for commentary about the spouses of political candidates," Obama said during an interview with KCRG-TV in Cedar Rapids. "My general view is those of us who are in the public life, we're fair game. Our families are civilians."
The rapid responses by both candidates' staffs showed the power of social media in shaping a campaign's narrative, and the sensitivity with which both campaigns view their efforts to appeal to women.
Various polls have indicated that Romney leads Obama among male voters, but that Romney trails the president among women by about 20 percentage points.
"This is an obvious ploy by both sides to try and demonstrate that they understand women voters and especially women dealing with families," said Jennifer Lawless, director of American University's Women and Politics Institute.
THE FIRST LADY TWEETS
The controversy mushroomed on social media on Thursday.
First lady Michelle Obama also commented on her own Twitter account, saying, "Every mother works hard, and every woman deserves to be respected."
"I think we can all agree - Democrats and Republicans - that raising children is an extremely difficult job," Carney said. "And that is true for all mothers, as well as fathers."
Women make up about 53 percent of the U.S. electorate. In a way, the controversy over Rosin's comments underscored the impact that former Pennsylvania Senator Rick Santorum had on the campaign, and the challenge he left for Romney when Santorum left the race this week.
Santorum is known for his strong opposition to abortion and contraception, as well as his belief that religion should play a larger role in public life. As Santorum made such issues a part of the debate in the Republican campaign, support among women for Romney - the Republican front-runner - declined.
"The GOP primary has had a focus on abortion, contraception, and other issues that disproportionately affect women," said Larry Sabato, director of the University of Virginia's Center for Politics. "Let's just say the Republicans haven't put themselves in a good light.
"The GOP has moved right along with its evangelical and Tea Party base, and Santorum also drove much of the social issue commentary," he said.
A SMALL BOOST FOR MITT ROMNEY?
Republican strategist Ron Christie said, "The reason this has enveloped the political establishment in the United States is that Ms. Rosen's remarks seemed indifferent to the struggles faced by women who elect to remain home with their children. I think the Romney campaign will get a short term boost from this controversy."
Susan Carroll, senior scholar at the Center for American Women and Politics at Rutgers University, said the flap allowed Mitt Romney to change the subject at a time when the Obama campaign has been hammering the Republicans for waging a "war on women" with a budget plan that would lower taxes for the rich while cutting programs that polls indicate are particularly important to women.
Social media, with its ability to grab a message and make it global within minutes, helped fuel the fire. Four years ago, Rosen's comments might have faded quickly, but Ann Romney's instant tweet - and the Democrats' quick responses - kept the issue alive.
"I do think what's going on Twitter is helping make the flap bigger than it otherwise would be," said Liz Mair, a Republican communications strategist.
Rosen eventually apologized on Thursday. "Let's declare peace in this phony war and go back to focus on the substance," she said in a statement.
"As a mom I know that raising children is the hardest job there is," Rosen said. "As a pundit, I know my words on CNN last night were poorly chosen." (Editing by David Lindsey and Cynthia Osterman)