WASHINGTON • The story of the Donald Trump dossier began in September 2015, when a wealthy Republican donor who strongly opposed the real estate magnate put up the money to hire a Washington research firm, Fusion GPS, to compile a file about his past scandals and weaknesses, according to a person familiar with the effort.
For months, Fusion GPS, headed by former Wall Street Journal journalist Glenn Simpson, gathered information and collated the files from the tycoon's past in business and entertainment, a rich target.
After Mr Trump emerged as the presumptive Republican nominee in May, the Republicans no longer wanted to finance the effort. Fusion GPS continued its work but for new clients - the Democratic supporters of Mrs Hillary Clinton.
In June, the tenor of the effort suddenly changed. The Washington Post reported that the Democratic National Committee had been hacked, apparently by Russian government agents, and a mysterious figure, "Guccifer 2.0", began to publish the stolen documents online.
Mr Simpson hired former British spy Christopher Steele, a top expert on Russia at Britain's spy service MI6 before he left in 2009, to build a file on Mr Trump's ties to Russia.
The two men, according to people who know them, had a similar dark view of Russian President Vladimir Putin, a former KGB officer.
As Mr Steele would not be able to travel to Moscow, he hired native Russian speakers to call informants inside Russia, and made surreptitious contact with his own connections in the country as well. He wrote up his findings in a series of memos that he began to deliver to Fusion GPS in June and continued at least until December, after the Nov 8 election was over. Though both men had no client to pay them, they did not stop what they believed to be very important work.
The memos described two different Russian operations. The first was a years-long effort to find a way to influence Mr Trump, perhaps because he had contacts with Russian oligarchs whom Mr Putin wanted to keep track of.
According to the memos, it used an array of familiar tactics: The gathering of "kompromat", compromising material such as alleged tapes of Mr Trump with prostitutes in a Moscow hotel, and proposals for business deals attractive to Mr Trump to win his allegiance.
The goal would probably never have been to make Mr Trump a knowing agent of Russia, but to make him a source who might provide information to friendly Russian contacts.
But if Mr Putin and his agents wanted to entangle him using business deals, they did not do it very successfully - Mr Trump has said he has no major properties there.
The second Russian operation described was recent: A series of contacts with Mr Trump's representatives during the campaign, in part to discuss the hacking of the Democratic National Committee and Clinton campaign chairman John Podesta. According to Mr Steele's sources, it involved, among other things, a late-summer meeting in Prague between Mr Michael Cohen, a lawyer for Mr Trump, and Mr Oleg Solodukhin, a Russian official who works for an organisation that promotes Russia's interests abroad.
Colleagues of Mr Steele say he was acutely aware of the danger that he and his associates were being fed Russian disinformation. Russian intelligence had mounted a complex hacking operation to damage Mrs Clinton, and a similar operation against Mr Trump was possible.
But much of what he was told, and passed on to Fusion GPS, was very difficult to check. And some of the claims that could be checked seemed problematic. Mr Cohen, for instance, said on Twitter on Tuesday night that he had never been in Prague; Mr Solodukhin, his purported Russian contact, denied in a telephone interview that he had ever met Mr Cohen or anyone associated with Mr Trump.
The President-elect on Wednesday cited news reports that a different Michael Cohen with no Trump ties might have visited Prague, and that the two Cohens might have been mixed up in Mr Steele's reports.
By early autumn, some of Mr Steele's memos had been given to the FBI, which was already investigating Mr Trump's Russian ties, and to journalists. An MI6 official said Mr Steele also passed the reports he had prepared on Mr Trump and Russia to British intelligence as he thought the information should not be solely in the hands of people looking to win a political contest.
Now, after the most contentious of elections, Americans are divided and confused about what to believe about the incoming President. And there is no prospect soon for full clarity on the veracity of the claims made against him.