A top adviser to Sen. Bernie Sanders' (I., Vt.) 2016 presidential campaign is accused of forcibly kissing a female staffer on the final night of the Democratic National Convention in July of that year, according to those familiar with the incident.

Robert Becker, who directed Sanders' Iowa campaign and served as deputy national field director, is alleged to have approached a female staffer at a Philadelphia bar where members of the campaign had gathered, Politico reports. Becker, in his late 40s at the time, told the staffer, who was in her 20s, that he had wanted to have sex with her "and made a reference to riding his ‘pole,' according to the woman and three other people who witnessed what happened or were told about it shortly afterward by people who did."

Becker grabbed the same woman's wrists later in the night, then moved his hands to her head and forcibly kissed her, putting his tongue in her mouth, according to the woman and other sources. The incident was not formally reported at the time because the campaign had concluded.

Over the past few months, Becker has been reaching out to possible staffers and visiting early primary states to lay the groundwork for a potential 2020 run by Sanders. The woman allegedly assaulted by Becker was one of those contacted, prompting her to inform senior Sanders advisers, including 2016 campaign manager Jeff Weaver, what she says happened the night of the convention.

"Candidates who allow people like Robert Becker to lead their organizations shouldn't earn the highest office in our government," said the staffer, who asked to remain anonymous out of fear of retaliation by Sanders and Becker loyalists.

"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. This can’t happen in 2020. You can’t run for President of the United States unless you acknowledge that every campaign demands a safe work environment for every employee and volunteer," the woman continued.

Becker denied the allegation.

"I categorically deny these allegations of improper and unprofessional conduct," Becker said in a statement. The allegation, he wrote, is "at odds with my recollection of a late evening filled with many hugs and kisses and tears and conversations about what’s next."

The Vermont senator's campaign committee, Friends of Bernie Sanders, said Becker "would not be a part of any future campaigns."

"To be clear: no one who committed sexual harassment in 2016 would be back if there were a 2020 campaign," said the committee, which also described Becker's alleged actions as "deplorable and fundamentally unacceptable."

Allegations of sexual misconduct and an "untenable and dangerous dynamic that developed during [the Sanders] campaign" have dogged the Vermont senator in recent weeks, according to Politico. Over two dozen 2016 campaign staff alumni wrote a letter seeking a meeting with Sanders to "discuss the issue of sexual violence and harassment on the 2016 campaign, for the purpose of planning to mitigate the issue in the upcoming presidential cycle."