Tucker Carlson pushed a Russian conspiracy theory suggesting the US blew up the Nord Stream pipeline.
The claim was then recycled by Russian state TV, and other far-right influencers.
Kremlin and US far-right propaganda often mirror each other.
Fox News host Tucker Carlson on Wednesday seized on the news that that the Nord Stream pipelines, which were built to channel gas from Russia to Western Europe, appeared to have been sabotaged.
Officials in Germany and other EU nations said the undersea pipeline - built by a consortium of European companies and Russia's state-run gas giant Gazprom - appeared to have been deliberately damaged. Western officials pointed to Russia as the likely culprit.
Their predominant theory is that the Kremlin was signaling that this vital line carrying energy to Europe is vulnerable to attack - a means to warn the EU over its support for Ukraine.
But Carlson had a different view.
"If you are Vladimir Putin, you'd have to be a suicidal moron to blow up your own energy pipeline," he said.
He pointed to remarks, by President Joe Biden from February, where he opposed activation of the pipeline.
Biden had said if Putin invades, "there will be no longer a Nord Stream 2, we will bring an end to it." Those remarks came as the US sought to tighten economic pressure on Russia before the war started. Nord Stream 2 is not in service.
Distorting the president's remarks and ignoring that context, Carlson said they could be construed to mean: "We will blow it up."
Within hours, the claim was being promoted by far-right influencers in the US, and pushed by the network of Russian state media networks, despite a lack of credible evidence that US warships or operatives had taken part.
Russian lawmakers on Wednesday called for Biden to address the allegations at the UN.
The case is another example of the lightning-fast reciprocity between far-right influencers in the US and Europe, and the Kremlin's propaganda machine.
Matt Gertz, a researcher with Media Matters, which monitors right-wing media, told Insider that Carlson's rhetoric and the Kremlin's propaganda have long mirrored one another.
"Carlson's coverage of the war in Ukraine has consistently aligned with that of Russia's government. He is part of a segment of the American right that is blithely uninterested in the suffering of Ukrainians, credulous of Vladimir Putin's stated motivations, and generally more interested in denouncing the US government than the Russian one," he told Insider.
Fox News did not respond to Insider's request for comment.
Defense and security expert Michael Clarke, a professor at the University of Exeter, told Insider that the clip of Biden speaking in February was "neither here nor there" as a form of evidence that the US masterminded the attack.
"What Tucker Carlson says is completely at variance with all the known factors," he said.
There is no publicly available evidence proving Russia was behind the attack. But Russian warships and submarines were spotted in the area and have the capability, via divers or mini subs, needed to place and detonate what's estimated to be hundreds of pounds of explosives to create pipeline breaks of this size.
Clarke added: "America would have far, far more to lose by doing something so stupid as this. The only government for whom it would make any sense would be the Russian government."
Carlson's take on the issue is merely "wish fulfillment," he said.
Isolationist, "America First" commentators like Carlson oppose US involvement in foreign conflicts, and have long harbored an admiration for Putin's Christian nationalist Russia, say experts.
Russia has been keen to exploit the admiration, tailoring conspiracy theories designed to appeal to the Western far-right.
Gertz, from Media Matters, pointed to a Russian government document obtained by Mother Jones in March telling state media outlets "it is essential to use as much as possible fragments of" Carlson's show because he "sharply criticizes the actions of the United States."
Since then, Carlson's attacks on US and western policy in Ukraine have been a weekly staple on Russian TV networks, and are praised by pro-Kremlin Russian pundits who say they show ebbing support for the war in the US.
And they may be right. One recent poll found that a majority of Americans want the war to come to a negotiated end.
How the Nord Stream claim spread
The journey taken by the Nord Stream pipeline Biden conspiracy theory is emblematic of the way pro-Russian propaganda travels.
A Wednesday tweet by Polish EU parliamentarian Radek Sidorski, which has since been deleted, triggered intense scrutiny from Russian state media and diplomats. It included a picture of the ruptured pipeline, with the caption: "Thank you, USA."
Sidorski's follow-up tweets appeared to attempt to clarify that the original tweet was a criticism of US support for the pipeline being built in the first place, but it was too late.
Russia's UN representative Dmitry Polyansky instantly amplified it, saying it made it "crystal clear who stands behind this terrorist-style targeting of civilian infrastructure."
Sidorski's spokesperson declined to comment or to clarify the lawmaker's meaning to Insider.
Maria Zakharova, spokesperson for Russia's foreign ministry, demanded that the EU answer to the tweet, per Russian state media agency TASS.
The claim was then picked up by Carlson, who combined it with the footage of Biden in February. This was then shared by US far-right influencers including Turning Point USA's Charlie Kirk, before being recycled by Russian state media, claiming its traction in the US gave it another layer of credibility.
In a particularly absurd laundering of the speculation, Russian state media outlet RIA Novosti then wrote an article compiling credulous and largely anonymous reader comments on UK conservative news outlet The Daily Mail. "Daily Mail readers accuse US of attacking Nord Stream," wrote the outlet.
The Washington Post noted that clips of Carlson's show were on continual rotation on Russia's main TV news networks Wednesday.
As the war enters its seventh month, one of the key questions is whether the Western alliance, on which Ukraine's military and financial support depends, will hold.
A strategy to split the West
The Kremlin and elements of the US far-right share the broader goal of undermining Western support for Ukraine, which has so far amounted to an estimated $15 billion.
The rhetorical attacks have the additional advantage of forcing the US to respond; State Department spokesman Ned Price called the claims "preposterous.
And the claims about Nord Stream could not come at a moment of higher tension between Russia and the West. Europe faces a painful winter as it attempts to wean itself off the supply of Russian energy, of which the Nord Stream pipelines were both a potent symbol and a flagship piece of infrastructure.
The West's economic sanctions of Russia have caused fuel inflation to spike in Europe, which has already led to protests in Prague, capital of the Czech Republic, this week.
The US is less dependent on Russian energy, but the Republican Party, whose "America First" wing remains powerful, is increasingly forecast to regain control of the House of Representatives in the November mid-terms.
Key members of the party have signaled they may seek to place obstacles in front of future multi-billion military aid packages to Ukraine.
It is these factions whose profile the Kremlin is likely seeking to boost, as it steps up its propaganda war and seizes on Western commentators to bolster its campaign.