Tomi Lynn Dorris, 50, an assistant attorney general who dated Dann's chief of staff, blamed "politics of destruction" for her withdrawal from the race in a statement she released yesterday.
O'Brien, 59, now appears to have a clear field in his run for a fourth term as county prosecutor, a position he has held since 1996.
O'Brien said the deadline to replace Dorris on the ballot was Aug. 20. William A. Anthony Jr., chairman of the Franklin County Democratic Party, said party leaders will meet tonight to discuss whether they can replace Dorris.
"That news is obviously disheartening to the party," Anthony said. "Tomi is a wonderful lady, but Tomi has to do what's best for her and her family."
O'Brien said he was disappointed that Dorris dropped out because "I had looked forward to presenting my strong record of accomplishments in the prosecutor's office to the public in this year's general election."
Dorris is on leave from her state post as executive director of the Ohio Peace Officers Training Academy in London. She formerly served as an assistant attorney general and chief counsel to the State Highway Patrol, as a domestic-relations magistrate, and a police officer at Ohio State University in the mid-1980s.
She said she had hoped to run a campaign on issues.
"Unfortunately, it has become clear that this race will not be about those substantive issues and ideas but will rather focus on the fact that I was once employed by former Ohio Attorney General Marc Dann."
Dorris noted that she had worked at the office for 11 years before Dann arrived.
She stressed that Dann "dishonored the office" of attorney general, and said that she wouldn't be able to raise enough money to take on O'Brien.
O'Brien said he was ready to defend his record. In an interview with Dispatch editors yesterday before Dorris' announcement, he cited initiatives he wants to continue, including combating street crime, gun violence and gangs. His office employs 112 assistant prosecutors and has a budget of nearly $3 million.
Robert Owens, an independent candidate for state attorney general, recently called for Dorris to resign her post as an assistant attorney general because of her ties to Dann, who resigned amid a sexual harassment scandal.
Others have criticized Dann for recommending Dorris to the police training academy commission last summer over a retired Cincinnati suburban police chief, even though Dann knew Dorris was dating his chief of staff at the time.
Dorris had not sought the police training academy position before her boyfriend, Edgar C. Simpson, recommended her for the post. Simpson lost his job in the Dann scandal.