The dustup arose in their debate the night before when Obama was asked whether his connection to Ayers raised politically damaging questions about his patriotism.
Obama struck back by calling attention to Bill Clinton's decision to grant clemency to two former Weather Underground members who - unlike Ayers - had been convicted of crimes from that era.
President Clinton's actions freed women who had been serving sentences of 40 years and 58 years after convictions on weapons, explosives and related charges.
Members of the Weather Underground, known initially as the Weathermen, claimed responsibility for a series of bombings, including non-fatal but destructive ones at the Pentagon and U.S. Capitol.
In addition, three members died when their bomb-making session at a New York City town house went awry in 1970, and several members were convicted in a botched 1981 Brink's truck ambush during which two police officers and a guard died.
Ayers was not implicated in the Brink's deaths and the two former members cleared by Bill Clinton were not convicted of killings.
THE SPIN: Obama said Ayers is "a guy who lives in my neighborhood" and not someone who has endorsed him or talked to him regularly.
"And the notion that somehow as a consequence of me knowing somebody who engaged in detestable acts 40 years ago when I was 8 years old, somehow reflects on me and my values, doesn't make much sense," Obama said.
Clinton said the relationship was deeper than that because both men served together on the board of a charity.
Ayers, she said, made comments "which were deeply hurtful to people in New York and, I would hope, to every American, because they were published on 9/11, and he said that he was just sorry they hadn't done more.
"And what they did was set bombs," she went on. "And in some instances, people died."
THE FACTS: Clinton's implication that Ayers made hurtful comments connected with the terrorist attacks is wrong.
By coincidence, a story about Ayers and what he called his fictionalized memoirs appeared in The New York Times on the day of the attacks.
The story was based on an interview he had done earlier, in Chicago, in which he declared, "I don't regret setting bombs," and "I feel we didn't do enough," even while seeming to dissociate himself coyly from the group's most destructive acts.
Clinton is correct that both men served together on the board of the Woods Fund, a Chicago-based charity that develops community groups to help the poor. Ayers joined the board in 1999 and is still on it. Obama left it in December 2002 after nine years.
Ayers was clearly more than someone Obama just ran into in the neighborhood on occasion. In the mid-1990s, when Obama was making his first run for the Illinois Senate, Ayers had Obama to his home to introduce him to others.
But a flub by Obama in the debate suggested he does not know him that well: He called Ayers an English professor. Ayers teaches education at the University of Illinois at Chicago and has been an education adviser to Mayor Richard Daley.
Ayers disappeared after the 1970 town house explosion, although he was not charged in that episode. He and his wife, Bernadine Dohrn, surfaced in 1980.
They both faced charges stemming from Chicago demonstrations in 1969 but his were dismissed for prosecutorial misconduct while she pleaded guilty to aggravated battery and bail-jumping.
THE SPIN: Obama said Clinton was not one to talk about guilt by association because "President Clinton pardoned or commuted the sentences of two members of the Weather Underground, which I think is a slightly more significant act than me serving on a board with somebody for actions that he did 40 years ago."
THE FACTS: Obama correctly sketched out the details of Bill Clinton's acts in the case. However, senior Obama strategist David Axelrod went too far Thursday when he said the two cleared by President Clinton had killed people. They were not convicted of that.
Bill Clinton created an uproar with New York lawmakers from both parties and with police when, on his last day in office, he granted clemency to Susan L. Rosenberg and Linda Sue Evans.
Rosenberg was sentenced to 58 years after being caught unloading 740 pounds of dynamite and weapons from a car in New Jersey in 1984. She was wanted on charges related to the deadly Brink's ambush but never tried on them, and Clinton's order released her after 16 years behind bars.
Evans was captured in 1985 along with one of the fugitives from the Brink's robbery, whom she was accused of harboring. Evans was sentenced to 40 years on a variety of weapons and terrorism-related convictions, including the 1983 Capitol bombing plot.
Although Hillary Clinton publicly disputed her husband's offer of clemency to Puerto Rican nationalists in 1999 because they had not sufficiently renounced violence, she is not known to have objected to his freeing of Rosenberg and Evans in 2001.
