Hillary Clinton refused to apologize Friday for using a private email account as US secretary of state despite an uproar dogging her presidential campaign, as she knocked Republican frontrunner Donald Trump.
Faced with eroding support, the Democratic hopeful for next year's election offered the most comprehensive public remarks yet about the email controversy.
But asked directly in a half-hour interview whether she wanted to apologize to the American people for her actions, Clinton demurred.
"I certainly wish that I had made a different choice," she answered, admitting she was "sorry" for the confusion caused.
"I take responsibility. I should have had two accounts: one for personal and one for work-related" emails.
But she insisted, as she has from the beginning, that "it was allowed and it was fully above board."
The lingering email saga has weighed on Clinton's popularity, with a Gallup poll released Friday showing her favorability rating at 41 percent, compared to 51 percent who view her unfavorably -- the lowest level since 1992.
But Clinton, who has long dismissed the email saga as a manufactured imbroglio, expressed optimism about her presidential bid and said she was confident of voters' trust.
"I am very confident that by the time this campaign has run its course people will know that what I've been saying is accurate," Clinton told MSNBC.
"The American people will know they can trust me when it comes to standing up to them and advocating for them and being their champion."
It was only the third sit-down television interview of her campaign, far fewer than just about all of her Democratic and Republican rivals.
She used the opportunity to slam her Republican rival Trump, saying his attack-mode campaign "is a bad development for our American political system."
Clinton signalled she was not going to participate in the bluster and showmanship that have been hallmarks of the real estate tycoon's campaign.
"He's great at innuendo and conspiracy theories and really defaming people," she said. "That's not what I want to do in my campaign, and that's not how I'm going to conduct myself."
As Clinton headed Friday to the island territory of Puerto Rico, it was her use of a private email account and home server in lieu of the official government email system while serving as top diplomat from 2009 to 2013 that dominated the news.
The Department of State, to which Clinton turned over 30,000 official emails in late 2014, has publicly released thousands of them in the interests of transparency.
Many contain information that has been retroactively classified, raising questions about whether Clinton was inappropriately sending and receiving highly sensitive material, and whether sufficient security measures were in place to protect her server from hackers.
The Federal Bureau of Investigation is examining the server to determine whether secret government data was compromised.
"At the end of the day I am sorry that this has been confusing to people and has raised a lot of questions," Clinton told MSNBC.
"But there are answers to all of these questions and I will continue to provide those answers," she said, adding that she was looking forward to testifying before a House panel on October 22.
Clinton said her lawyers meticulously combed through her 60,000 emails, ultimately handing over more than 30,000 of them to the State Department.
Her server was then wiped clean.
"I was asked 'Do you need to keep your personal emails?' and I said, 'No, we don't. You can delete those,'" she told MSNBC.
Asked if she was concerned at her lacklustre poll figures, Clinton said "it certainly doesn't make me feel good."
Warning signs have emerged in New Hampshire, where her approval rating has slid and polls show liberal Senator Bernie Sanders running neck and neck against her.
The state holds the second nominating contest in the nation, after Iowa, and a victory there could help pave her path to the presidential nomination.
Clinton had been the Democratic frontrunner in 2008 before losing out to then-senator Barack Obama. Asked if she was worried a similar opportunity could now be slipping through her fingers, she was firm.
"I don't feel that," she said. "I am very excited and very energized by the campaign that I'm running."
Further fuelling uncertainty, Vice President Joe Biden has begun publicly discussing the prospect his own White house bid.
"The most relevant factor in my decision is whether my family and I have the emotional energy to run," Biden, who lost his son Beau to cancer in May, said Thursday.