On Jan. 10, 2017, BuzzFeed News published a photo rendition of a 35-page memo titled "U.S. Presidential Election: Republican Candidate Donald Trump's Activities in Russia and Compromising Relationship With the Kremlin."

Those who were online that evening remember the jolt. Yes, these were just allegations, but perhaps this was the Rosetta Stone of Trump corruption, touching everything from dodgy real estate negotiations to a sordid hotel-room tryst, all tied together by the president-elect's obeisance to President Vladimir Putin of Russia.

Sure, the memo provided little hard evidence or specific detail, but, BuzzFeed said, it had "circulated at the highest levels of the U.S. government" and had "acquired a kind of legendary status among journalists, lawmakers and intelligence officials." This, along with tantalizing tidbits like "Source A confided" or "confirmed by Source E," gave it a patina of authenticity, especially to those unaware that spycraft often involves chasing unverified information down dead ends. Any caveats – even BuzzFeed's own opening description of the allegations as "explosive but unverified" – could be dismissed as a kind of obligatory cautiousness.

That memo, soon to become known as the "Steele dossier" when a former British intelligence officer named Christopher Steele was publicly identified as its author, would inspire a slew of juicy, and often thinly sourced, articles and commentaries about Mr. Trump and Russia.

Now it has been largely discredited by two federal investigations and the indictment of a key source, leaving journalists to reckon how, in the heat of competition, so many were taken in so easily because the dossier seemed to confirm what they already suspected.

Many of the dossier's allegations have turned out to be fictitious or, at best, unprovable. That wasn't for want of trying by reporters from mainstream and progressive media outlets. Many journalists did show restraint. The New York Times's Adam Goldman was asked by the Washington Post media critic Erik Wemple about two years ago how reporters should have approached an unverified rumor from the dossier. He responded, "By not publishing."

Others couldn't wait to dive in.

Two reporters in McClatchy's Washington bureau, for example, wrote that the special counsel Robert Mueller had found evidence for one of the most tantalizing bits of the dossier, that Mr. Trump's lawyer Michael Cohen secretly visited Prague during the 2016 campaign. That would have been a key link in the claim that he was there to coordinate campaign strategy with the Russians. It wasn't true.

Over time, the standards for proof diminished to the point that if something couldn't be proved to be false, the assumption was that it was probably true. As MSNBC's Rachel Maddow once put it: A number of the elements "remain neither verified nor proven false, but none so far have been publicly disproven."

Or journalists would take Mr. Trump's other serious misdeeds and tie them to the dossier. So his alleged sexual relationship with Stormy Daniels, who appeared in pornographic films, became the backup for the dossier's claim of a lurid round with prostitutes in a Moscow hotel. "The count is growing higher and higher of porn actresses," Slate's editor at the time, Jacob Weisberg, said on MSNBC, adding, "The whole picture starts to be more plausible, the picture that's painted in the dossier." Natasha Bertrand, who was then a staff writer at The Atlantic, chimed in, "It makes it much more plausible that Trump did go to Russia and he did have these kinds of sexual escapades with prostitutes."

The dossier's credibility suffered a grievous blow in December 2019, when an investigation by the Department of Justice's inspector general found that F.B.I. investigations "raised doubts about the reliability of some of Steele's reports." The F.B.I. "also assessed the possibility that Russia was funneling disinformation to Steele," the report said, adding that "certain allegations were inaccurate or inconsistent with information gathered" by investigators.

Then, this month, a primary source of Mr. Steele's was arrested and charged with lying to the F.B.I. about how he obtained information that appeared in the dossier. Prosecutors say that the source, Igor Danchenko, did not, as The Wall Street Journal first reported, get his information from a self-proclaimed real estate partner of Mr. Trump's. That prompted a statement promising further examination from The Journal and something far more significant from The Washington Post's executive editor, Sally Buzbee. She took a step that is almost unheard-of: removing large chunks of erroneous articles from 2017 and 2019, as well as an offending video.

So where did much of the press go wrong?

The first problem was this: There is no doubt that Mr. Trump had long curried Mr. Putin's favor and that he and his family were eager to do business in Russia. Moreover, Mr. Mueller showed, and filed indictments that explained, how the Russians interfered in the 2016 campaign by targeting voter-registration systems, hacking into Democrats' emails and taking advantage of Facebook and other social media companies to foment dissent and unrest.

Mr. Trump's choice of Paul Manafort to serve as his campaign chairman reinforced the idea that he was in the thrall of Russia. Those fears were borne out when a bipartisan Senate committee found Mr. Manafort to be a "grave counterintelligence threat" because of his ties to a Kremlin agent. So, given all those connections, it was easy to assume that the dossier's allegations must also be true. The distinction between what journalists assume and what we verify is often the difference between fiction and reality.

Journalists also had to deal with the fact that many of the denials came from confirmed liars. The night that BuzzFeed went live with the dossier, Mr. Cohen told the website Mic that the material was "so ridiculous on so many levels" and that "this fake-news nonsense needs to stop." (Mr. Cohen later pleaded guilty to federal charges including lying to banks and Congress, but even after he provided evidence against Mr. Trump, he said the Prague allegation was false.)

The day after the dossier came out, Mr. Trump told reporters: "It's all fake news. It's phony stuff. It didn't happen." (Washington Post fact-checkers would eventually catalog more than 30,000 Trump falsehoods during his term in the White House.) When a well-known liar tells you that something is false, the instinct is to believe that it might well be true.

The situation also became complicated because some reporters simply didn't like or trust Mr. Trump or didn't want to appear to be on his side. He had been berating journalists as charlatans while seeking their acclaim; calling on legislators to "open up our libel laws" to make it easier to sue news organizations; and launching personal attacks, especially on female reporters of color. In a perfect world, journalists would treat people they don't like the same way they treat those they do like, but this is not a perfect world.

As the former Times reporter Barry Meier writes in his book "Spooked," "Plenty of reporters were skeptical of the dossier, but they hesitated to dismiss it, because they didn't want to look like they were carrying water for Trump or his cronies."

None of this should minimize the endemic and willful deceptions of the right-wing press. From Fox News's downplaying of the Covid-19 threat to OAN's absurd defense of Mr. Trump's lies about the election, conservative media outlets have built their own echo chamber, to the detriment of the country.

But news organizations that uncritically amplified the Steele dossier ought to come to terms with their records, sooner or later. This is hard, but it's not unprecedented. When The Miami Herald broke the news in 1987 that the Democratic presidential candidate Gary Hart was seeing a woman other than his wife, the paper followed that scoop with a 7,000-plus-word examination of its investigation, which showed significant flaws in how the paper surveilled its target.

More than two decades ago, after New York Times articles identified a scientist at Los Alamos as being investigated for having a role in a spying scheme, which federal investigators were unable to substantiate, the paper ran both an extensive editors' note and an article that included details about how its reporting had gone astray.

Newsrooms that can muster an independent, thorough examination of how they handled the Steele dossier story will do their audience, and themselves, a big favor. They can also scrutinize whether, by focusing so heavily on the dossier, they helped distract public attention from Mr. Trump's actual misconduct. Addressing the shortcomings over the dossier doesn't mean ignoring the corruption and democracy-shattering conduct that the Trump administration pushed for four years. But it would mean coming to terms with our conduct and whatever collateral damage these errors have caused to our reputation.

In the meantime, journalists could follow the advice I once got from Paul Steiger, who was the managing editor of The Journal when I was editing articles for the front page. Several of us went to his office one day, eager to publish a big scoop that he believed wasn't rock solid. Mr. Steiger told us to do more reporting – and when we told him that we'd heard competitors' footsteps, he responded, "Well, there are worse things in this world than getting beaten on a story."

Bill Grueskin, a professor of professional practice and former academic dean at Columbia Journalism School, has held senior editing positions at The Wall Street Journal, The Miami Herald and Bloomberg News.