One of the more unfortunate effects of the Trump-Russia investigation — and there have been many — is the weakening of traditional standards of argument and proof in the public debate over allegations that the Trump campaign conspired with Russia to fix the 2016 election. (Just for the record: It didn’t.)

In particular, angry disputes about the president have done terrible harm to the principle that an investigator, be it a journalist or a prosecutor, should meet at least some standard of proof before leveling an accusation.

Two examples: First is the so-called Steele dossier, the collection of wild allegations against Trump compiled by former British spy Christopher Steele on behalf of the Hillary Clinton campaign and the Democratic National Committee.

Steele’s unfounded accusations — that there was a yearslong “well-developed conspiracy” between Trump and Russia, that Trump accepted “a regular flow of intelligence from the Kremlin,” and that Russian spies taped Trump watching prostitutes perform a kinky sex act in a Moscow hotel room in 2013 — circulated throughout law enforcement and political circles starting in the summer of 2016. That just happened to be the time the Clinton campaign and some in the media began accusing Trump of “colluding” with Russia to gain an advantage in the election.

Top Clinton staff received updates on Steele’s material. Then they accused Trump of collusion. FBI investigators, who also had the dossier, were trying to confirm it. They failed.

Without evidence to prove any of the dossier’s most serious allegations, a new standard of proof emerged: The allegations were legitimate because they had not been proven untrue.

Leading figures in politics and journalism adopted the new standard. “Not a single revelation in the Steele dossier has been refuted,” said Sen. Dianne Feinstein, top Democrat on the Senate Judiciary Committee. “(I’m) aware of nothing in the Christopher Steele dossier that has been shown to be false,” said Harvard law professor Laurence Tribe. “So far with this dossier, nothing yet has been proven untrue,” said Chuck Todd, host of NBC’s “Meet the Press.”

The new Trump standard turned the old standard — can an allegation be proven true? — on its head.

It’s not surprising that commentators, especially those with partisan motives, would adopt such a low standard. It was surprising when — and this is example No. 2 — Trump-Russia special counsel Robert Mueller upended the justice system’s traditional norms by declaring that his investigation, while not accusing the president of committing a crime, also could not exonerate him.

“If we had confidence after a thorough investigation of the facts that the president did not commit obstruction of justice, we would so state,” Mueller said in his 448-page report. “Based on the facts and the applicable legal standards, we are unable to reach that judgment. Accordingly, while this report does not conclude that the president committed a crime, it also does not exonerate him.”

Mueller repeated the point in his recent public statement. “If we had confidence that the president clearly did not commit a crime, we would have said so,” he said. “We did not, however, make a determination as to whether the president did commit a crime.”

It was a mind-blowing moment for some Justice Department veterans. Since when do prosecutors hand out certificates of exoneration to the people they investigate? (Answer: They don’t.) Since when has “not exonerated” been an accepted legal outcome — as in, “How does the jury find the defendant? We find him not exonerated.” (Answer: Never.)

Mueller, like Feinstein and Tribe and Todd before him, changed widely accepted standards, casting the shadow of guilt on Trump without formally accusing him of wrongdoing. Except Mueller, unlike the senator, the law professor and the journalist, wielded the prosecutorial power of the United States. Given the length and thoroughness of his investigation, Mueller’s no-exoneration verdict carried a lot of weight in the public debate. Except that it didn’t mean anything, while at the same time it suggested to the public that the president had committed some unspecified offense.

Trump’s critics often accuse him of violating the norms that make our society and government work. Yet in their discussion of the dossier, some of those critics violated essential norms of fairness and accuracy. And in Mueller’s no-exoneration gambit, a storied figure in American law enforcement abandoned one of the most important standards of justice. The damage done could last a long time.

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