Hillary Clinton has admitted that she should have fired an adviser accused of sexual harassment during her 2008 presidential campaign.
Burns Strider was initially docked pay and told to seek counselling but was later fired from a campaign group after again being accused of harassment.
Mr Strider has not commented on the allegations.
Mrs Clinton posted the statement moments before President Donald Trump began his state of the union speech.
It has prompted some speculation that she was seeking to bury her apology in the storm of media coverage around the address.
The 30-year-old woman who made the complaint shared an office with Mr Strider, the New York Times said when it broke the story of the claims last week.
It said that, according to three former campaign officials, she had told a campaign official that Mr Strider had rubbed her shoulders inappropriately, kissed her on the forehead and sent suggestive emails.
When her complaint was investigated, two advisers, including her campaign manager, recommended Mr Strider be fired, but instead Mrs Clinton moved her to a new role, while Mr Strider stayed in place.
The matter has raised questions about Mrs Clinton’s judgement and stated commitment to women’s advancement.
In her lengthy Facebook statement, Mrs Clinton says: “I’m being asked as to why I let an employee on my 2008 campaign keep his job despite his inappropriate workplace behaviour.
“The short answer is this: If I had it to do again, I wouldn’t.”
She says she understands the scrutiny of her decision to retain Mr Strider given her work to “support and empower women”.
Mrs 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.
“He needed to be punished, change his behaviour, 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,” Mrs Clinton writes.
She 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,” Mrs Clinton writes.
But she points out that the events took place long before the “seismic shift” in social attitudes towards sexual harassment.
Mr Strider was Mrs Clinton’s faith adviser and has continued to send her scripture readings over recent years, the New York Times said.