GCHQ, the British intelligence agency, has furiously denied the White House's claims that Barack Obama may have asked UK spies to help wiretap Trump Towers.
The furore began when Sean Spicer, the White House press secretary, made the astonishing allegation during a press conference on Thursday, where he cited a Fox News legal analyst as his source.
That analyst is Andrew Napolitano - or, as Fox News refers to him, "Judge Nap."
Who is Andrew Napolitano?
The 66-year-old is a former New Jersey Superior Court who became a media commentator after hanging up his robes.
He most frequently appears on Fox and Friends, but also discusses current affairs on the O'Reilly Factor, Fox Busness Network and the Kelly File.
A pro-life libertarian, he is also the host of a right-wing talk radio programme, Freedom Watch.
What did he claim?
On March 14, Fox & Friends invited Mr Napolitano onto the show to discuss claims that Barack Obama had ordered a wiretap on Donald Trump's campaign headquarters.
These allegations are fiercely disputed. At no point has the Trump administration ever brought forward any evidence to support their claims. A spokesman for Barack Obama has also flatly denied them.
During this programme, Mr Napolitano said that if Mr Obama spied on Trump Towers, there may not be any evidence to prove it.
He went on to say that when a president orders a surveillance operation, it will usually leave a paper trail of some form.
He then claimed that in Mr Obama's case, he may have gone to a British intelligence agency to seek external help, so as not to leave any evidence that a wiretap took place.
"Three intelligence sources have informed Fox News that President Obama went outside the chain of command," he said. "He didn't use the NSA, he didn't use the CIA, he didn't use the FBI, and he didn't use the Department of Justice."
How does he know this?
Mr Napolitano is an experienced legal affairs expert who began his career back in 1975. Several of his rulings as a superior judge are considered influential.
However, as a media commentator, he has no official links whatsoever to US intelligence services. He can only provide his own personal opinions on legal affairs.
Though he referred to three "intelligence sources" during the controversial segment of the programme, it is unclear who these sources were.
His claims are therefore closer to being "hearsay" than concrete evidence that could be used to trigger a formal investigation into the wiretapping allegations.
What happens now?
Mr Napolitano is licking his wounds after GCHQ issued a statement which utterly dismissed his analysis, branding the claims "ridiculous."
If, as widely expected, there is no evidence in existence to support the administration's wiretapping claims, it is unlikely he will broach the subject on TV anytime soon.
According to US media reports, Fox News has quietly pulled him off the air following a massive backlash against the channel for airing the unfounded allegations.
It is extremely rare for a British intelligence agency to issue a public statement on sensitive security affairs, especially those linked to foreign powers.