Hillary Clinton has admitted that she should have fired her adviser, Burns Strider, who was accused of harassment during her 2008 presidential campaign.
Burns Strider was initially docked pay and told to seek counseling but was later fired from a campaign group after again being accused of harassment.
He has not commented on the allegations.
Hillary Clinton posted the statement moments before President Donald Trump began his state of the union speech.
Her move has prompted some speculation that she was seeking to bury her apology in the storm of media coverage around the address.
According to New York Times, the 30-year-old woman who made the complaint shared an office with Burns Strider when it broke the story of the claims last week.
The report said that, according to three former campaign officials, she had told a campaign official that Burns Strider had rubbed her shoulders inappropriately, kissed her on the forehead and sent suggestive emails.
When the woman’s complaint was investigated, two advisers, including her campaign manager, recommended Burns Strider be fired, but instead Hillary Clinton moved her to a new role, while Strider stayed in place.
The matter has raised questions about Hillary Clinton’s judgment and stated commitment to women’s advancement.
Hillary Clinton said in a statement posted on Facebook: “I’m being asked as to why I let an employee on my 2008 campaign keep his job despite his inappropriate workplace behavior.
“The short answer is this: If I had it to do again, I wouldn’t.”
The former presidential candidate says she understands the scrutiny of her decision to retain Burns Strider given her work to “support and empower women”.
Hillary Clinton then goes on to explain her reasoning in detail.
She decided to do so, she says, “because I didn’t think firing him was the best solution to the problem.
Hillary Clinton wrote: “He needed to be punished, change his behavior, and understand why his actions were wrong. The young woman needed to be able to thrive and feel safe.
“I thought both could happen without him losing his job.”
Hillary Clinton also says she has “reached out” to the woman in question: “The fact that [she] felt heard and supported reinforced my belief that the process worked – at least to a degree.”
However, she points out that the events took place long before the “seismic shift” in social attitudes towards harassment.
Burns Strider was Hillary Clinton’s faith adviser and has continued to send her scripture readings over recent years, the New York Times reported.