Holstering his bombast for the moment, President Donald Trump has so far refrained from trashing Christine Blasey Ford, the woman accusing US Supreme Court nominee Brett Kavanaugh of sexual assault when both were teenagers in suburban Washington DC in 1982.

It’s a measure of the low bar set by this White House that Mr Trump’s restraint is worth noting: It’s like complimenting a teenager for not swearing in church.

Nevertheless, it is a departure from Mr Trump’s customary tactics of denial, demean, defame and disparage, so for that it’s newsworthy.

It’s also too late. A bitten tongue can’t hide the damage Mr Trump has already inflicted on US institutions, and it’s the Kavanaugh controversy that will soon reveal that destruction.

And once again, it involves the FBI.

Ms Ford has insisted that before she testifies before the Senate Judiciary Committee, the FBI investigate her charges against Mr Kavanaugh. Her demand is a direct response to the chaos that surrounded the 1991 Supreme Court confirmation hearings of Clarence Thomas.

Mr Thomas, an African-American judge nominated by Republican President George HW Bush to replace Civil Rights legend Justice Thurgood Marshall, appeared to be headed towards a narrow confirmation.

Suddenly a former colleague, Anita Hill, came forward with allegations that Mr Thomas, her former boss at a federal agency, engaged in highly sexualised office banter, talking about porn, bestiality, his sexual exploits, women’s breast sizes and, infamously, a pubic hair on his Coke can.

Ms Hill’s appearance before the committee, almost exactly 27 years ago, riveted the nation. (I remember pulling over on a lonely Utah highway, struggling to find a radio station out in the high desert carrying her live testimony).

It was the highest stakes of “he said, she said,” a sudden cage match of sexual and racial politics (like Thomas, Hill is black) that no one, least of all the senators on the committee, were prepared for.

Mr Thomas pushed back hard, famously calling Ms Hill’s testimony “a high-tech lynching,” summoning up the darkest shame of America’s racist past.

The committee chairman, Democratic senator Joe Biden (yep, that Joe Biden) struggled to control the proceedings and the fallout. Nowadays, he acknowledges he failed. A key reason, he and others note, is that he didn’t stop the hearings and look more deeply into Ms Hill’s allegations –namely, by calling in the FBI and having it launch a full investigation.

Such an investigation would have at least cooled the partisan fever on both sides of the Thomas drama. It would have slowed a runaway process that history has shown was haphazard and unworthy of such an important appointment. And it would have provided more information on which to make a judgement.

Back in that more innocent era, their findings would have been seen by most Americans as genuinely impartial. At the very least, an FBI investigation would have given cover to senators who were stuck having to choose between two protagonists, one of whom was lying.

Today, this option has been soiled beyond repair. Even if Ms Ford gets her wish and committee chairman Senator Chuck Grassley calls in the FBI (which seems unlikely), the FBI’s reputation is in tatters. Mr Trump’s ceaseless and baseless attacks have managed to poison too many Americans against it.

I’ve written before about the FBI’s dubious history, its illegal surveillance against civil rights leaders and anti-war activists. And fired director James Comey’s own self-regard hasn’t helped.

But in instances like this, its role as the nation’s detective agency is essential in finding the truth. Mr Trump, however, has disparaged the bureau and its leadership since his inauguration, revelling in his own mad conspiracy theories and accusing Mr Comey and other officials of crimes, lies and treason.

If he had evidence, of course, Mr Trump should do something. He has none. But he has succeeded in destroying the last best chance America has of rising above the partisan howl to somehow find the truth.

Maybe Ms Ford gets her wish and the FBI is called in. Maybe the vote on Mr Kavanaugh is delayed while a full investigation takes place. That would be encouraging.

But should that investigation prove damaging to Mr Kavanaugh, you know who’ll be the first to open his mouth.

Larry Hackett is the former editor-in-chief of People magazine, and a current contributor to the US morning television news program Good Morning America