FBI Director James Comey requested yesterday that the Justice Department publicly refute President Trump’s claims that President Obama had “tapped” phones at Trump Tower in the runup to the November election, according to the New York Times.

Trump had suggested that the behavior rose to “Watergate/Nixon” levels of illegality.

That official rebuttal has not yet occurred — although Comey has now effectively produced his own refutation, thanks to leaks to the Times (whose reporting has not been confirmed elsewhere, as of early Sunday evening).

The background: On Saturday morning, Trump claimed on Twitter that Obama had ordered the phone lines in Trump Tower tapped during the presidential campaign. Trump cited no evidence for this claim, which appeared to spring from a Breitbart article that itself provided no evidence.

The Times article puts the extraordinary nature of Comey’s request in context:

A statement by the Justice Department or Mr. Comey refuting Mr. Trump’s allegations would be a remarkable rebuke of a sitting president, putting the nation’s top law enforcement officials in the position of questioning the truthfulness of the government’s top leader. The situation underscores the high stakes of what the president and his aides have unleashed by accusing the former president of a conspiracy to undermine Mr. Trump’s young administration.

The Times story gives two main reasons that some at the FBI, notably Comey, may be interested in getting the Justice Department to knock down the allegations. The first is that — under one reading of Trump’s tweets — they imply that the bureau acted as an Obama crony, illegally circumventing the judicial process and mounting a politically motivated investigation against Trump. Comey wants that idea refuted swiftly and categorically.

The second reason is more subtle, and seems to hinge on there having been no wiretap at all at Trump Tower — even a court-approved one. (This part of the Times piece seems less clear.) The FBI, the Times says, is worried about public impressions if it becomes widely believed that it did gain the legal authority to tap Trump’s phones, because the public might assume the FBI does have damaging information about Trump’s ties to Russia: “Senior F.B.I. officials are said to be worried that the notion of a court-approved wiretap will raise the public's expectations that the federal authorities have significant evidence implicating the Trump campaign in colluding with Russia's efforts to disrupt the presidential election.”

Now, it’s certainly possible the FBI was investigating close associates of Trump during the campaign. The BBC reported in January that the Foreign Intelligence Surveillance Court granted the FBI a warrant allowing it to track interactions between Russian banks.

That is obviously a far cry from the idea that President Obama himself ordered that the FBI exact retribution on his political foe. Thanks to this leak to the Times, the FBI can be added to the long list of those denying Trump’s wiretapping claim — one that now includes President Obama, former Director of National Intelligence James Clapper, senior intelligence officials, and some congressional Republicans.