Most likely, the dossier against Trump was cribbed from the Internet and other sources of gossip, speculation, and invention. In legal controversies, I have seen even absurdly expensive, supposedly fact-based "investigative reports" by national PI firms staffed by former federal agents fall apart on examination because they were at heart nothing but dressed up gossip collected from former colleagues who were treated to meals and drinks.
Even worse, the point of Chris Steele's dossier against Trump was to generate and spread about lurid but superficially plausible fiction that could be rumored and reported by the news media against Trump without them being easily vulnerable to a suit for libel. Thus Buzzfeed reported on the dossier as of public interest because it was briefed by the US intelligence community. Even though Buzzfeed also treated the dossier as of doubtful veracity. CNN then reported on the Buzzfeed story and acted as its tout so that the underlying allegations would be spread far and wide.
Trump and his company ought not to settle for this week's victory but should seek a definitive resolution by suing Chris Steele and his firm in Britain under their more plaintiff favorable libel laws. Michael Cohen and the Trump organization should be the plaintiffs, with Trump's personal claim added by way of assignment. Then Steele can be forced to admit that it was all a fiction and to provide a full accounting of his role and of who else was involved.
Unfortunately, if this is not done, this smear against Trump is likely to be resurrected by his enemies in the news media and on the Left. The Trump as Russian agent claim is too useful to abandon, and some form of blackmail by the Russians is so easy to imagine that the dossier will be suspected to be true in some sense even if some details were gotten wrong and Trump bullied the news media off the trail. After all, the dossier has to be true in some sense because it was compiled by a former MI-6 agent. Or so Trump's enemies will argue when it is useful and effective to do so.
A former MI-6 agent who now own$ and run$ a company that provide$ to it$ cu$tomer$ exactly what they want: DIRT.................