This could be serious. Seems like there was a drunken legislator who touched a woman's breast in an elevator and it was a really big deal. This will depend upon if there is a third party willing to testify that he/she saw the assault happen and it was not consensual. It is a fact that he said/she said incidents are very tough for law enforcement to do anything about because either or both people could be lying. But an eyewitness who was not involved in the incident takes it to a whole new level.
There is no need to worry about presumption of innocence or guilt because no suspect has been charged or named yet. But it appears that after investigation the police believed there was enough to take to the DA.