"To the women in our campaign who were harassed or mistreated I apologize", Sanders said at a news conference Thursday.
Politico reported at the end of 2018 that Sanders aides had called a meeting with the senator to discuss allegations of sexual harassment during the campaign in an attempt to mitigate the damage to a potential future candidacy.
A top adviser for Bernie Sanders' 2016 presidential campaign stands accused of forcibly kissing a woman staffer and making a reference to her riding his "pole" at a hookah bar after the Democratic National Convention had concluded, Politico reported Wednesday.
Thursday's statement emerged hours after a Politico story that detailed new accusations against a top Sanders adviser in 2016 who is already taking steps towards working on a possible 2020 Sanders campaign in early voting states like Iowa.
"Our standards, our procedures, our safeguards, were clearly inadequate, " Sanders said. "What they experienced was absolutely unacceptable and certainly not what a progressive campaign, or any campaign, should be about". "I apologize", Sanders tweeted on Thursday.
"Candidates who allow people like Robert Becker to lead their organizations shouldn't earn the highest office in our government", she said.
He apologized "to any woman who felt that she was not treated appropriately, and of course if I run, we will do better next time", but went on to say that he was unaware of the allegations because he "was a little bit busy running around the country trying to make the case".
Senator Bernie Sanders has apologised to female staff members on his 2016 USA presidential campaign who allege they were mistreated by male aides.
Mr Becker denies any harassment, and no criminal charges have been filed.
"It just really sucks because no one ever held him accountable and he kept pushing and pushing and seeing how much he could get away with", she told the outlet.
In a statement sent to VTDigger before Sanders had issued his apology, the senator's primary campaign committee, Friends of Bernie Sanders, said Becker's alleged conduct is "deplorable and fundamentally unacceptable". They added: "To be clear: no one who committed sexual harassment in 2016 would be back if there were a 2020 campaign".
Allegations that male members of his campaign had harassed and discriminated against female campaign workers have been circulating for weeks as the senator weighs a potential second presidential run. Female staffers also claimed they were paid significantly less than their male counterparts or subordinates.
The Sanders situation hit headlines after November's midterm elections, in which the #MeToo women's movement - propelled by female voters' frustration with President Donald Trump, who himself stands accused of assault or harassment by multiple women - helped sweep Democrats to victory.