(CNN) Sen. Bernie Sanders and senior aides met on Wednesday with a group of women and men who requested a face-to-face discussion about what they described as "the issue of sexual violence and harassment" on the Vermont independent's 2016 presidential primary campaign.

The meetings, which stretched for almost a full day, began near Capitol Hill on Tuesday evening and picked up after the full group convened for breakfast on Wednesday morning. Their goal, according to participants on both sides of the table, was to confront past failures while forming more robust plans of action for future campaigns, including a potential second run by Sanders in 2020.

Former campaign manager Jeff Weaver, who will not return to the role if Sanders runs again in 2020, and the high-level aides asked for in the letter, including Ari Rabin-Havt, Caryn Compton, Arianna Jones and Shannon Jackson, were in attendance, according to a source present, along with dozens of former campaign staffers.

Sanders, who was present for a midday session of the meeting, told CNN the discussions were "private" when asked about them afterward on Capitol Hill. Sanders wife, Jane, also took part.

The source said Sanders participated in the midday session with the former campaign workers and outside "facilitators" drafted in to lead a series of conversations and workshops. The letter, which was leaked to Politico late last year, described his presence at the proposed meeting as a "critically important" to the process of creating a "'gold standard' harassment policy" complete with "tangible next steps."

A former staffer for the Sanders campaign, who asked her name not be revealed so she could discuss the private meeting, told CNN Sanders was present for "about an hour" and described him as "conciliatory." She said he opened his remarks with an "honest apology."

"It was clear that he came to listen and to have us be heard," the former staffer said. "He heard many powerful stories and I think he understood that these are not just one-offs and I got the sense that there was a real desire from him to not see a repeat of this ever again."

Sanders has yet to decide on whether he will pursue a second bid for the Democratic presidential nomination, and the spate of allegations is unlikely to dissuade him from running, allies say. He has not been implicated in any of the accusations and there has been no suggestion he was made aware of them during the campaign. But the charges have led to new questions over his management skills and the lack of diversity on the 2016 staff, which former campaign manager Jeff Weaver has conceded was "too male and too white."

There is no organized push to dissuade Sanders from running, but the revelations about mistreatment of women on the 2016 campaign has stoked concerns, even among some supporters, over his ability to secure and broaden his coalition -- especially in a year when so many other progressives are expected to run. Sen. Elizabeth Warren is already in and voters at her events in Iowa and New Hampshire, in interviews with CNN, often seemed torn over whether they would support her or Sanders in 2020.

In Washington last week, Sanders addressed a group of protesters at a rally organized by the AFL-CIO in support of federal workers impacted by the ongoing government shutdown. He was received warmly, but there were also notes of concern in the crowd.

"I think he could've handled (the sexual harassment claims) a little bit better," Democrat Julie Appelstein, a college student in Washington, D.C. by way of New Hampshire, told CNN. "I think that it is a really important issue and, I think with the Me Too movement especially, it is going to come up in campaigns. I do think it is going to come up in the 2020 election and I don't think we should run a candidate like that with that much risk."

In Sanders' corner, though, are committed activists and volunteers -- many of them holdovers from the bitter 2016 primary -- who are actively encouraging him to run. Over the weekend, "People for Bernie"and "Organizing for Bernie" launched house parties designed to signal to Sanders the depth of his support. Organizers said there were more than 400 in total, across all 50 states, Puerto Rico and one in the Bahamas, with around 3,500 likely volunteers on hand.

"There was definitely a sexual harassment problem, in part because at every stage of the campaign there were more men than there were women," a female former staffer who did not attend the meeting told CNN.

She said the true test for Sanders will be come in how he builds a future campaign, especially in his choice to replace Weaver, who not reprise his campaign manager role in 2020.

"Who (Sanders) surrounds himself with will be very important. I think it is important he put women in leadership, there needs to be more people of color," the woman said. "If he runs in 2020 it will have to be different, the world is different and he needs a campaign that can adapt."

At the meetings in Washington, Sanders staff and those who signed the letter were joined by a trio of independent "facilitators" -- two of them, Pamela Coukos and Jenny Yang, a former chair of the Equal Employment Opportunity Commission, from a firm called "Working IDEAL" and another, Rene Redwood, who is the chief executive of Redwood Enterprise and was named by Hillary Clinton's presidential campaign in February 2016 as a prominent African American woman supporter.

In an interview afterward, Yang called the meetings "a first step in a broader process" and not just an airing of "tough experiences." The goal, she said, was to "use that knowledge and energy to really improve processes moving forward and to serve as a model for campaigns to use around the country."

Another facilitator, who asked not to be named but also helped lead the sessions, said Sanders was "here to listen and we appreciated him participating with open ears and open heart."

"We're at a point in our society where folks are speaking up and saying that we can't talk about inclusive cultures and then practice exclusion," the facilitator, who has been in the political sphere for three decades, told CNN. "It's a systemic challenge for all campaigns."

The letter from former staffers that set the summit in motion touted the "unique camaraderie" that existed within Sanders' 2016 team and said their request to meet over the allegations had been spawned by "an ongoing conversation on social media, in texts, and in person, about the untenable and dangerous dynamic that developed during our campaign." Among the stated goals: their hopes of "mitigating the issue in the upcoming presidential cycle -- both in the primary and potential general elections campaigns for 2019 and 2020."

The Friends of Bernie Sanders, his campaign committee, in a statement on December 30 thanked "the signers of the letter for their willingness to engage in this incredibly important discussion" and listed steps -- including new reporting structures and a 1-800 number for staffers who needed to lodge private complaints -- the organization had taken during Sanders' 2018 Senate re-election campaign to install "more robust policies and processes regarding discrimination and harassment."

After the New York Times published a report days later detailing allegations of sexual harassment and pay disparities on the campaign, the committee again responded by saying it "does not and will not tolerate harassment or discrimination of any kind."

That night, January 2, Sanders pledged in an interview with CNN's Anderson Cooper that, if he were to run again, "We will do better next time."

But in denying any knowledge of the allegations during the 2016 campaign, Sanders said that he "was a little bit busy running around the country trying to make the case" -- a response critics viewed as flip and allies worried would overshadow his apology. Eight days later, after an aide who worked in multiple states for the 2016 campaign was accused of forcibly kissing a woman who had previously worked for him, Sanders apologized again, this time addressing the allegations at the end of a news conference on Capitol Hill.

First he thanked "from the bottom of my heart" the women who were "harassed or mistreated" for speaking out, then -- this time in greater detail -- spoke about his regrets.

"What they experienced was absolutely unacceptable, and certainly not what a progressive campaign or any campaign should be about," Sanders said. "When we talk about -- and I do all of the time -- ending sexism, and ending all forms of discrimination, those beliefs cannot just be words. That, they must be based in day to day reality and in the work that we do. And that was not the case, clearly not the case, in the 2016 campaign."