Bob, can't Democrats be sexual assault victims? One of Franken's accusers was actually a conservative talk radio host. Nobody made an issue of her politics.
As to the FBI, you mistake what I am saying. Yes, sexual assault/attempted rape are state, not Federal crimes. However, it is the FBI's job to do a background check of Federal nominees for fitness of character. It is SOP. Since it is the office of President making the nomination it has to be at his request to investigate the candidate's background.
They typically look at criminal records, credit records, employment records, they interview your past employers, your current friends, past friends, and your family members. Any accusations that a nominee committed a crime would be thoroughly investigated before clearing that candidate. Now that it has been alleged that the nominee committed a crime, Trump refuses to request the FBI to update the fitness review.
If he did, the FBI would interview both Ford and Kavanaugh. They would interview Kavanaugh's friend, Mark Judge, and the other yet unnamed individual. They wouldn't allow them to issue blanket denials like that never happened. They would ask specific questions like did you know this girl, did you attend a party with this girl, were you drinking, were you and Mark Judge ever alone with this girl. At any time in the past were you aware of these accusations. When were you first made aware of these accusations?
They would ask the victim who she told about the incident and when. They would interview those people. They would ask for any documentation like the therapist's notes. They would talk to the therapist.
They would offer all parties the option to take FBI administered polygraphs. After they did all of this, they would make a determination if the allegation was credible based upon the interviews, materials provided and how forthcoming each party was. The purpose wouldn't be to charge Kavanaugh with a crime but rather to determine if he is morally fit for a lifetime appointment.
Here is the thing. Trump and the Republicans knew about this and knew it was a credible accusation. That is why they had the letter prepared in advance with the 65 women he went to high school with. The only person that could have told them about this accusation in advance and the need to solicit character reviews from women he went to high school with would have been Kavanaugh himself.