Obama conceded that Clinton would be a better president than George Bush. "But that's not saying very much," he quickly added.
Obama said all three candidates -- including presumptive Republican nominee John McCain -- would be better than Bush.
Clinton took issue with Obama's apparent olive branch for the Arizona senator.
"We need a nominee who will take on John McCain, not cheer on John McCain," she said.
Obama also launched a new ad, responding to Clinton's previous attacks and accusing her of "11th-hour smears, paid for by lobbyists."
Clinton's campaign countered with another attack ad of its own, charging, "He couldn't answer tough questions in the debate, so Barack Obama is making false charges about Hillary's health plan."
Supporters of both campaigns have gone even further.
A retired major general who supports Obama raised Clinton's claims that she dodged sniper fire during her 1996 trip to Bosnia. Walter Stewart called that a "dishonor," and said it should disqualify her from laying wreaths at the Tomb of the Unknown Soldier.
A Clinton supporter is circulating a mailer raising the issue of Obama's acquaintance with Bill Ayers, a Chicago professor who was once a member of the violent Weather Underground.
The mailer, created by union activist Rick Sloan of the International Association of Machinists, claims Republicans will "channel Joe McCarthy" in the fall, turning Obama's "change we can believe in" into "change no patriotic American could stomach."
Both campaigns have disavowed those particular statements.
But Democratic Party activists in Pennsylvania said they worry the bitterness could make it difficult to mend fences once the dust settles.
"This has gotten so bad this year, I'm not sure people can forget about it and put it behind themselves after Tuesday," said Joe Morgan, a Democratic committeeman for Berks County.
He said the supporters are worse than the candidates when it comes to vindictive attacks.
"The bitterness and anger they have toward people who are not supporting their candidate is something I have never seen before," he said.
Morgan has been writing his own blog on the race, so at first he decided to remain neutral. He said Obama fans in particular were incensed with him for doing so. His tires were slashed and a complaint was lodged with the Internet service provider for his blog. Morgan is now supporting Clinton.
But as the candidates criss-crossed the state this weekend making their closing arguments to the voters, there was one sign that even the most bitter divisions could be healed.
The Pittsburgh Tribune Review endorsed Hillary Clinton. The endorsement itself is no surprise, except that the owner and publisher of the paper is Richard Mellon Scaife, the billionaire heir to the Mellon fortune whom Clinton once accused of masterminding the "vast right-wing conspiracy" against her and her husband.
Apparently all of that is now water under the bridge. No hard feelings at all.
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