"She knows better. Shame on her. Shame on her," Obama told an audience at a union hall here.
The Illinois senator has spent three days on the defensive after comments he made at a San Francisco fundraiser were disclosed that suggested working class people are bitter about their economic circumstances and "cling to guns and religion" as a result.
Obama reiterated his regret for his choice of words at the fundraiser but suggested they had been twisted and mischaracterized. He said he'd expected blowback from GOP nominee-in-waiting John McCain, but had been "a little disappointed" to be criticized by Clinton.
Then, laughing along with the union audience, Obama noted that Clinton seemed much more interested in guns since he made his comments than she had in the past.
"She is running around talking about how this is an insult to sportsmen, how she values the Second Amendment. She's talking like she's Annie Oakley," Obama said, invoking the famed female sharpshooter immortalized in the musical "Annie Get Your Gun."
He continued: "Hillary Clinton is out there like she's on the duck blind every Sunday. She's packing a six-shooter. Come on, she knows better. That's some politics being played by Hillary Clinton."
Clinton has told campaign audiences that she supports the rights of hunters. Saturday, she reminisced about learning to shoot on family vacations in Scranton, where her father grew up. She's also said she once shot a duck in Arkansas, where she served as first lady.
Clinton, who is trailing Obama in the popular vote and pledged delegates, has pounded Obama since Friday, when audio from his San Francisco appearance was posted on The Huffington Post Web site. She hoped the comments might give her a new opening to court working-class Democrats less than 10 days before the Pennsylvania primary on April 22, which she needs win to keep her campaign going.
At the San Francisco fundraiser, Obama tried to explain his troubles in winning over some working-class voters, saying they have become frustrated with economic conditions: "It's not surprising, then, they get bitter, they cling to guns or religion or antipathy to people who aren't like them or anti-immigrant sentiment or anti-trade sentiment as a way to explain their frustrations."
Campaigning in Scranton on Sunday, Clinton denounced those remarks yet again as "elitist and divisive" and suggested they would alienate voters in Pennsylvania and other states holding primaries in the coming weeks.
"Senator Obama has not owned up to what he said and taken accountability for it," she told reporters during an informal news conference outside a home. "What people are looking for is an explanation. What does he really believe? How does he see people here in this neighborhood, throughout Pennsylvania, Indiana, North Carolina, other places in our country? And I think that's what people are looking for, some explanation, and he has simply not provided one."
Indiana and North Carolina vote on May 6.
"You don't have to think back too far to remember that good men running for president were viewed as being elitist and out of touch with the values and the lives of millions of Americans," Clinton added, referring to John Kerry, the defeated 2004 Democratic nominee.
"I think it's very critical that the Democrats really focus in on this and make it clear that we are not (elitist). We are going to stand up and fight for all Americans," Clinton said.
Fighting back, Obama said Clinton's history proved she was not as sensitive to the concerns of blue collar voters as she tried to project.
"I just have to remind people of the track record," Obama said, noting Clinton accepted campaign contributions from PACs and drug and insurance industry lobbyists, which he does not.
"This is the same person who took money from financial folks on Wall Street and then voted for bankruptcy bill that makes it harder for folks right here in Pennsylvania to get a fair shake. Who do you think is out of touch?" Obama said.
"This is the same person who spent a decade with her husband campaigning for NAFTA, and now goes around saying she's opposed to NAFTA," Obama said, referring to the North American Free Trade Agreement that is widely unpopular in blue collar communities.
The Clinton campaign issued a quick retort to Obama's comments.
"For months, Barack Obama and his campaign have relentlessly attacked Hillary Clinton's character and integrity by using Republican talking points from the 1990s," said spokesman Phil Singer. "The shame is his. Senator Clinton does know better she knows better than to condescend and talk down to voters like Senator Obama did."
Obama planned to further address the question of which candidate was most in touch with middle-class voters in a speech Monday to The Associated Press annual meeting in Washington.