Washington (CNN) Kirsten Gillibrand's Senate office restructured a top aide's role in the wake of sexual harassment allegations between two other staffers last year, a Gillibrand aide tells CNN, the clearest sign yet that the office acknowledges mistakes had been made after the investigation into the allegations was completed and the accused staffer was not fired.

A Gillibrand aide acknowledged that post-investigation, there had been human error in communicating with the woman who made the accusations. The aide said that Deputy Chief of Staff Anne Bradley, who made the error, would no longer have any involvement with investigations or personnel cases in the office. Bradley's title did not change. The controversy around the office's handling of a sexual harassment allegations has undercut a key reason for Gillibrand's rise to national prominence: Her stands against sexual assault and her championing of the #MeToo movement. The New York Democrat is now open to accusations that she did not live up to the standards she has sought to set for others. The controversy also comes at a perilous time for Gillibrand's 2020 effort: Her presidential exploratory committee, announced in January, has yet to gain much traction in national or statewide polls, and the second-term senator has failed to garner much support from leaders in her home state. Gillibrand was defiant in defending the office's handling of the investigation on Monday when pressed by reporters, but changing Bradley's role is the first acknowledgment by Gillibrand's team that some errors had been made. Read More On Monday, Politico reported and CNN later confirmed that a woman who worked in Gillibrand's Senate office accused a senior staffer of sexual harassment in 2018. After Gillibrand's staff investigated the allegations and a subsequent allegation of intimidation, the accused staffer -- Gillibrand military adviser Abbas Malik --was not fired, leading the accuser to resign from Gillibrand's office over the handling of the matter. Instead, Malik was punished by not receiving a promotion or boost in salary he was in line to get. Politico reported that after it began looking into the story and found further allegations of derogatory comments against Malik, Gillibrand's office decided to fire Malik. In a letter the accuser wrote to Gillibrand, her then-chief of staff and now campaign manager Jess Fassler and general counsel Keith Castaldo, the accuser details her interactions with Bradley following the investigation and said that Bradley and Fassler informed her that it was "too much of a 'he said, she said' situation." "On Tuesday, July 31, 2018, Anne came into my office and said that 'Jess told Abbas that he could have fired him for a number of reasons but isn't going to. So he should consider himself lucky.' Thinking I had the full support of the office, I was deeply confused and saddened by this," the accuser wrote. "Later that afternoon, I decided to discuss this with Jess and Anne. Jess responded to me by saying, 'You could also be fired at any minute, for any reason.'" The accuser wrote in her letter that she "offered my resignation because of how poorly the investigation and post-investigation was handled. I hope your office will choose to handle cases like this with more sensitivity and understanding in the future." Gillibrand has remained strident throughout the controversy, defending her and her top aide's handling of the matter and deflecting questions about whether her closeness to Malik clouded her decision-making on the issue. "I will always look to improve my processes with my new chief of staff, with her experience, we will look to see how we can improve," Gillibrand told reporters on Monday. "But this investigation was thorough and professional, and the allegations were taken seriously from the very first day." She added: "The sexual harassment claims did not rise to the level of sexual harassment." Gillibrand went on to say she told the accuser that she "loved" and supported her. But the accuser clearly did not feel that support was sufficient and referenced Gillibrand's own record of championing women accusers to critique the senator in her resignation letter. "I trusted and leaned on this statement that you made: 'You need to draw a line in the sand and say none of it is O.K. None of it is acceptable,'" the accuser wrote. "Your office chose to go against your public belief that women shouldn't accept sexual harassment in any form and portrayed my experience as a misinterpretation instead of what it actually was: harassment and ultimately, intimidation." The handling of the situation did not sit well with a number of Democratic activists, including Angela Rye, a CNN commentator. When asked for her thoughts on the situation, Rye called it "pretty incredible." Sexual harassment is "black and white until our feelings get involved," Rye said. "It's black and white until it's somebody we know. Until it's somebody who we say they would never do that. ... But what happens when you say something like that, and it automatically debunks the real, credible stories of so many other real women victims." Gillibrand refuted the idea that her judgment was clouded by her closeness to Malik, telling reporters on Monday that she stood by the way they handled the investigation and that Malik had been "punished severely." "He was denied a promotion, he was denied pay, his desk was removed and he was unable to have unsupervised contact with" the accuser, she said. Organizations and advocates who push for more stringent rules around sexual assault and harassment widely credit Gillibrand's work on the issue, with many believing she is one of the most steadfast supporters they have on Capitol Hill. That is one reason why it may be difficult to see her handling of the accusations against Malik gaining traction in a Democratic primary; one of Gillibrand's Democratic opponents would have to use it against her, something a Democrat may be reluctant to do. Still, the timing creates a headache for the senator: Her 2020 effort has sputtered since announcing and the story involves her top campaign aide and longtime adviser, Fassler. Additionally, it rekindles talk of her handling of allegations against Sen. Al Franken, who resigned after a series of sexual misconduct allegations against him. Gillibrand was the first senator to call on Franken to resign after allegations of unwanted touching and kissing were made against him. Though more than 20 Democrats would eventually call on Franken to step down, Gillibrand led the charge by saying it would be "better for our country" if Franken stepped down and sent a message that "any kind of mistreatment of women in our society isn't acceptable." That decision has rankled some Democrats who were fond of the Minnesota Democrat, but Gillibrand has defended her call for Franken's ouster and used it on the campaign trail to demonstrate how she is willing to stand up for victims even when the accused is a close friend. Aides are also confident that Gillibrand will get a boost when she officially announces a presidential campaign, an announcement that is expected to come soon. Fassler, after working as Gillibrand's chief of staff, became her campaign manager earlier this year, building on his years of work with the New York senator. According to the letter from the accuser, Fassler played a central role in the investigation. A separate Gillibrand aide defended Fassler's handling of the matter, saying he "repeatedly demonstrated his respect and gratitude for the employee, and he was grateful she came forward." "The investigation determined that the individual was also responsible for an unrelated office policy violation, which as the top manager he had a responsibility to raise, while also making clear that she would not be disciplined to ensure that she and other employees felt safe to report any personnel issues in the future," the aide said. Fassler did not respond to request for comment. Despite the confidence shown by Gillibrand aides, the accuser's letter makes clear she did not feel supported by Fassler's comments. "I felt defeated, not just from the humiliation and pain that the harassment had brought me, but that in attempting to seek appropriate disciplinary actions for my harasser, my experience was devalued. I was devalued," she wrote. Gillibrand said Monday, after the story had been reported, that she maintains "complete confidence" in Fassler.