Lieutenant Governor Justin Fairfax, a 39-year-old African-American, has meanwhile been accused of forcing himself sexually on a woman 14 years ago. According to Tyson's account, Fairfax and she met on the first day of the Convention and became friends.
Should Cox be elevated to governor, Republican control in both houses of Virginia's legislature would extend to the state's executive branch in the run-up to the 2020 USA presidential election.
She said "Mr Fairfax's attack was premeditated and aggressive" and the details "are similar to those described by Dr Vanessa Tyson".
The woman, Meredith Watson, says the alleged assault happened while they were both undergraduate students at Duke University.
Additionally, the firm said it has statements from former classmates corroborating that Watson had immediately told friends about the alleged rape.
"Ms. Watson shared her account of the rape with friends in a series of emails and Facebook messages that are now in our possession", the release states.
Fairfax has denied the allegation and called for an investigation. It is demonstrably false.
In a statement from his spokesman, Faifax said he has "never forced myself on anyone ever" and demanded a "full investigation into these unsubstantiated and false allegations". "It is obvious that a vicious and coordinated smear campaign is being orchestrated against me", he said.
Democrats had until now stopped short of calling for Mr Fairfax to quit, but the latest allegation opened the floodgates on Friday.
Calls for Northam's resignation among Virginia's Democratic establishment were almost universal early on, with at least five Democratic candidates for the White House joining the chorus. "Everyone, presidential candidates, Democratic candidates here and everywhere, are going to have to wrestle with this". She left a campus party when he arrived, and he followed her out. She seems to be a credible person, she has no partisan motive to lie, she's not asking for money, she's not doing the interview circuit, she claims a specific date and place that the assault occurred, the accused admits to having been with her behind closed doors at that time and place.
Democrats in Richmond and in Washington say the next moves may largely depend on what black state legislative leaders push for.
Virginia's two USA senators and seven Democratic congressmen released a joint statement saying the sexual assault accusation must be investigated, and Herring must continue to have "in-depth discussions" if he is to regain the public's trust.