In the febrile atmosphere of this transition, there are lurid reports circulating about Donald Trump that are both potentially explosive and entirely unproven.
It is important to underline this point: These new allegations are not only unverified but possibly unverifiable.
But nor can we ignore them - in fact they must have some credibility because otherwise they wouldn't have reached the desk of the US President.
They formed part of a briefing last week to both President Obama and President-elect Trump.
Last night they were being widely discussed on US TV news networks and on social media worldwide.
This is what we know - or at least, what we think we know:
There are US intelligence reports that claim the Russians may have highly compromising material on the President-elect;
This alleged material was gathered by a former British intelligence agent, who was asked to compile the report by Trump's Republican and Democratic opponents;
The alleged material suggests that Trump's personal conduct with Russian women during a visit to Moscow has left him highly compromised;
There are also reports that there may be links (being examined by the FBI) between Trump advisers and Russian businessmen assumed to be connected to Moscow's intelligence agencies.
Where does this leave us?
Firstly, Trump is dismissing the allegations as completely false. This was his response on Twitter last night:
Secondly, Trump will need to address these claims at his press conference - his first in many months - in New York later today.
Finally, it guarantees the Trump presidency - already wrestling with questions of legitimacy after its loss of the popular vote - will begin amid a new torrent of controversy.
We are entering uncharted territory, with a President-elect facing a crisis of confidence even before he has taken office.