Paul Woodwrote for the BBC on Trump's "compromising" claims":
Donald Trump has described as "fake news" allegations published in some media that his election team colluded with Russia - and that Russia held compromising material about his private life. The BBC's Paul Wood saw the allegations before the election, and reports on the fallout now they have come to light.
The significance of these allegations is that, if true, the president-elect of the United States would be vulnerable to blackmail by the Russians.
I understand the CIA believes it is credible that the Kremlin has such kompromat - or compromising material - on the next US commander in chief. At the same time a joint taskforce, which includes the CIA and the FBI, has been investigating allegations that the Russians may have sent money to Mr Trump's organisation or his election campaign.
Claims about a Russian blackmail tape were made in one of a series of reports written by a former British intelligence agent, understood to be Christopher Steele.
As a member of MI6, he had been posted to the UK's embassy in Moscow and now runs a consultancy giving advice on doing business in Russia. He spoke to a number of his old contacts in the FSB, the successor to the KGB, paying some of them for information.