Speaking to MSNBC’s Chuck Todd the same day, BuzzFeed’s editor in chief, Ben Smith, explained the decision to publish the report. It had been circulating among journalists and politicians for weeks, he said, and so had become an “object that is in play, that is having consequences for the way our elected leaders are acting.”

Mr. Smith likened publishing the material to quoting conspiracy theorists who believed that President Obama was not born in the United States. A key difference, however, was that in the “birther” case, journalists could say definitively that the conspiracy theorists’ claims were untrue. They had actual facts to report. In publishing the dossier on Mr. Trump, however, BuzzFeed stated only that it had been unable to verify the allegations. It could not provide readers any help determining the veracity of the report — except, perhaps, the readers’ own opinions.

In the essay “Truth and Politics,” Hannah Arendt pointed out that truth, unlike opinion, is “beyond agreement, dispute, opinion or consent.” Truth doesn’t change depending on how many people accept it. Writing in 1967, Arendt observed a worrisome tendency for factual truth to be countered with opinion and thereby apparently transformed into opinion — becoming subject to debate. She was worried that facts were being disputed out of existence. We are now witnessing the same process in reverse: Dispute is coming first, as though the opinions of a large enough number of people who found this or that allegation “believable” could produce facts where none had been observed or verified.

I have been here before. As Mr. Putin consolidated power in Russia, it became more and more difficult for journalists to report facts. We lost access to many institutions, while others became progressively less trustworthy. With the president often lying or obfuscating and with all of the government brought under the control of the executive branch, we could no longer look to the courts, the police or other state institutions to learn or corroborate facts — if we could get anyone to talk to us or give us documents at all. Reality became squishy.

The same process is gaining speed in the United States. The president-elect lies habitually. The news media are losing access to information — not just because the incoming administration is even less transparent than the outgoing one, and is openly hostile to journalists, but also because full control of both houses of Congress is allowing the Republican Party to make the legislative process more opaque.

At the same time, there is a crisis of trust in the intelligence services: Many people argue that the F.B.I. acted to influence the presidential election; some (including me) believe the combined intelligence services’ report on Russia’s role in the election does not stand up to scrutiny. On top of it all, a large part of the country appears to have firmly replaced reality with a worldview based on opinions.

There are no ready recipes for dealing with this predicament. The media scholar Jay Rosen has urged journalists to move to a model that assumes less access and relies less on “players.” But this cannot compensate for a loss in available, reliable information that journalists can report. It seems inevitable that old rules like “multiple independent sources” will be dropped because they have become untenable. But from my experience in Russia, I know that this doesn’t end well. What is lost in the balance is truth.