"What precise foreign-policy experience is she claiming that makes her qualified to answer that telephone call at 3 a.m. in the morning?" Obama asked of the former first lady at a town-hall meeting. It was a reference to dueling television ads over who would exercise superior judgment in responding to a national emergency in the middle of the night.
The Illinois senator also sought to ease lingering Internet-fed concerns about his religion, in particular whether he was a closet Muslim.
"I am a devout Christian. I have been a member of the same church for 20 years. I pray to Jesus every night," he declared at an earlier appearance in the rural southern Ohio town of Nelsonville. He said he wanted to halt "confusion that has been deliberately perpetrated."
Unlike Clinton, who has been barnstorming Ohio, Obama had only two events in the state on Sunday and was spending the night in hometown Chicago. He heads to Texas on Monday for a final day of campaigning before awaiting returns on Tuesday in San Antonio.
His aides said privately that they felt they had a good shot at a win in Texas, but were less certain about Ohio, where they braced for a possible loss.
The two senators came close to running into each other in a Columbus suburb, where Clinton spoke at one high school and Obama spoke several hours later at another. Obama supporters boasted of a much larger crowd.
CBS News correspondent Jim Axelrod reports that in one part of Westerville, Ohio, Clinton told supporters: a candidate must be more than a good speaker.
"Sometimes I finish a speech," she said, "and people come up to me and they say, 'Oh, that was so inspiring and so wonderful and it made me feel so good.' I say 'Well, that's great but that's just words.' Our job is to make a difference."
From another part, Obama had a different message: Clinton's experience didn't stop her from voting wrong on Iraq.
"To this day, she won't even admit her vote was a mistake or that it was even a vote for war," he told potential voters. "So besides the decision to invade Iraq, we're still waiting to hear Senator Clinton tell us what precise foreign policy experience that she is claiming that makes her prepared to answer that phone call at three in the morning."
Obama said his opposition to the war in Iraq in 2002 was not a single speech - as Clinton has asserted - but a series of remarks during his 2002 successful Senate campaign.
Obama criticized Clinton expressly for failing to read the classified National Intelligence Estimate on Iraq's weapons capabilities, a report available at the time of her October 2002 vote authorizing the Iraq war. "She didn't give diplomacy a chance."
"When it came time to make the most important foreign policy decision of our generation the decision to invade Iraq Senator Clinton got it wrong," Obama said.
He said that Sen. Jay Rockefeller, a fellow Democrat from neighboring West Virginia, had read the intelligence estimate as a member of the Senate Intelligence Committee. However, Rockefeller wound up voting for the war resolution.
Rockefeller, who is now chairman of that committee, endorsed Obama on Friday and campaigned with him on Saturday.
Rockefeller called Obama "brilliant" and "well grounded" and prepared to take the reins as commander in chief.
The Obama campaign also lined up a conference call for reporters with various Democratic foreign-policy experts who asserted his ability to inspire and lead, his good judgment on Iraq, and ticked legislative accomplishments. It was an effort to undercut Clinton's claim that Obama foreign-policy experience was shallow.
Neither candidate forgot the fact that Ohio is a state hit hard by job loss, and both hit on the economy in their stump speeches today.
"I couldn't believe the prices on the gas stations I was driving by … $3.68 in the poorest part of Ohio," Clinton marveled. "We need a President who gets it and who says, 'wait a minute, we're going to do something about this!"
"I will invest $150 billion over ten years in establishing a green energy sector that will create up to five million new jobs," said Obama.
With Ohio and Texas both widely seen as "must win" for Clinton, she took a quick trip to New York last night to be on "Saturday Night Live."
"Oh, the campaign is going very well." Clinton told comedian Amy Poehler, dressed as a Hillary lookalike, "Very, very well. Why? What have you heard?"
"Nothing," Poehler answered, just a little too quickly.
Both Clinton and Obama will fly to Texas tomorrow where Obama has erased a long-standing Clinton lead. Political scientist James Henson says voters like to be on the winning team - and Obama's won 11 in a row.
"Texans like to think of themselves as different, Henson said. But we're not that different in the sense that people are taking a second look at this thing."
"And moving towards Obama?" asked Axelrod.
"It feels like it," Henson nodded.
Still, Axelrod reports, it's too close to call in Texas. As for Ohio, where the polls do show Clinton in a little bit of a stronger position, one top neutral Democrat there says that Obama does have the momentum, he is shrinking the lead, but the question is, does he have enough time?