In my early career, as a state prosecutor outside of Detroit, I dreaded handling sexual assault cases. After my first 10 cases, the ache in my stomach would come like clockwork as I sat down to open a sexual assault file for the first time. Evidence in sexual assault cases is often thin and trying to bring justice to a victim in a case with thin evidence is a prosecutor’s worst nightmare.

“He said/she said” has become part of the lexicon of language used to discuss sexual assault cases for a reason. A significant number of sexual assaults occur with just two people in the room, the perpetrator and the victim. But, that’s not what occurred in the allegation of sexual assault made by Christine Blasey Ford against supreme court nominee Brett Kavanaugh.

In a recent interview, Ford claimed that Mark Judge, a close friend of Kavanaugh’s, was an eyewitness to the sexual assault. According to Dr Ford, Mark Judge observed the assault and drunkenly jumped on top of Kavanaugh while he was assaulting her, giving Ford the opportunity to escape.

To a prosecutor, learning of a third-party eyewitness to an alleged sexual assault is a boon. Apparently, this additional evidence has had the opposite effect on the Senate judiciary committee.

Rather than embracing testimony from Judge as a means of finding the truth about Ford’s allegation, the Republican Senate judiciary committee chairman, Charles Grassley, has scheduled a hearing for Monday and has refused to call Judge as a witness.

There is a sleight of hand that has allowed Grassley to turn a blind eye to this pivotal piece of evidence. Mark Judge sent a letter to Grassley’s committee saying he had “no memory” of the incident Ford disclosed. Judge also said he never saw Kavanaugh “act in the manner Dr Ford describes”. Other Republican senators, including Lindsey Graham, have fallen in line behind Grassley, saying that there is “no reason” to call Judge to testify because they already know what he will say – exactly what he said in his letter.

But wait. If Mark Judge’s letter to the judiciary committee is sufficient to make its Republican members accept the contents of the letter at face value, why don’t they do the same for the letter Ford sent to ranking committee member Diane Feinstein? The answer simple: Republican members of the judiciary committee want to believe Judge, not Ford.

Prosecutors know that one of the most common ways a witness tries to avoid testifying against family or friends is by saying “I don’t remember”. But nothing makes a memory rush back faster than questioning under oath, after the witness has just heard the words “under penalty of perjury”.

Given that Mark Judge published a memoir in which he admitted to spending much of his youth “wasted” on alcohol, it may be that he truly does not remember the events described by Ford. However, Judge’s testimony would allow the committee to determine if Judge is claiming that he is certain Ford’s account of events did not happen. Or, would Judge acknowledge that his frequent state of being “wasted”, at parties like the one where Ford says the assault took place, prevent him from remembering the incident, even if it took place as Ford described. These are two very different positions and Judge’s letter almost appears to go out of its way to not distinguish one from the other.

As it stands, there is a dangerous, if not insidious, precedent created by Grassley’s failure to subpoena Judge. Grassley has allowed Judge to testify unofficially, through the letter written by his attorney and released to the public. The Republican-led judiciary committee is using Judge as a ghost witness to influence public opinion against Ford. Although they are employing a more gentle touch, Republican members of the committee are doing to Ford what they did to Anita Hill, 27 years ago, when they refused to allow three independent witnesses to testify in support of Hill’s version of events.

Equally troubling is the White House’s failure to direct the FBI to investigate Ford’s accusation. Donald Trump has said that the FBI does not do investigations into allegations like those raised by Dr Ford. He’s wrong. The FBI routinely investigates all aspects of a judicial nominee’s background that may affect his fitness to sit as a judge. The FBI could investigate DrFord’s allegations in a matter of days.

By refusing to call Mark Judge as a witness, and refusing to direct the FBI to investigate, Republican members of the Senate judiciary committee and the president are in lockstep. They have ensured that there are only two witnesses to an allegation of sexual assault against a man who will receive a lifetime appointment that will a shape a generation. One witness says yes, the other no.

“He said/she said” is an unfortunate reality of many sexual assault cases; it is not something to which we should aspire. The Republicans have manufactured a “he said/she said” standoff and are using their own handiwork to make good on a promise to stack the supreme court with conservative judges.

What is perplexing about the spectacle that will continue into next week’s hearings is that Trump has a whole list of Federalist Society-approved supreme court candidates who all see the world through their lens. So, it’s unclear why the White House is ride or die on Brett Kavanaugh.

Whatever the reason, Kavanaugh is already on the track. Events of the last few days have made it clear that the president, and the Republican members of the Senate judiciary committee, are not going to let a woman’s allegation of sexual assault, and a search for the truth, derail the train.

Michael J Stern was a state prosecutor outside of Detroit and a federal prosecutor for 25 years in Detroit and Los Angeles

• This article was amended on 22 September 2018, to correct an error by which Ford was referred to instead of Judge.