The 'Steele Dossier' was a compilation of several people from Fusion GPS and people with links to those who were with Fusion GPS

The Mechanics of Deception:

Much has been said and written about Christopher Steele’s authorship of the notorious document that alleges Russia-Trump collusion. According to Glenn Simpson of Fusion GPS (who plead the Fifth and only spoke through his lawyers), Steele was hired by them in June 2016 to gather information about “links between Russia and [then-presidential candidate] Donald Trump.” Pursuant to that business arrangement, Steele prepared a series of reports styled as intelligence briefings, some of which were later compiled into a collection of documents and published by a number of media outlets and later become known as the “Trump dossier.”

On the face of the dossier, it appears that Steele gathered his data from multiple sources in Russia, former Soviet union (FSU) countries, and the US. He then edited the raw intelligence—which seems to be a combination of conversations and notes—organized it in a summarized brief format, and published/leaked it in parts or in its entirety on a spiraling schedule.

Image 1: The Dossier events and publication schedule

My initial impression reading the dossier was that the writing was sloppy and that it did not resemble an intelligence report. It exhibited multiple writing styles and writers, both English and non-English speakers, and it was assembled in haste. I also thought that in many ways, it paralleled the plot line of the Dreyfus Affair. As in the case of the “dossier” and the Bordereau from the Dreyfus case, the Trump dossier was presented as undeniable proof of collusion. Yet, it’s uncertain who composed it, how it was collected, or even if the document is genuine. 

Just like its nineteen century French predecessor, the Trump dossier too had a powerful social and political impact in the US. Its content has dominated the news and has raised substantial questions about the rule of law, the political impartiality of senior federal career bureaucrats, and the true extent of the separation of powers in government.

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This is a long piece that ties together the myriad writers who actually composed the material in the dossier.  Steele was evidently hired to dress it up and make it look like an intelligence report.  Clarice Feldman also comments on the piece.  The ties of all the characters involved are somewhat familiar names to those who have followed the Clinton's in the past and there are even ties to Stephan Halper who was evidently used as a spy in the Trump campaign by the FBI.  Yaacov Apelbaum wrote The Mechanics of Deception and clearly did a better job than the FBI in looking at the content of the dossier.  The Congressional investigators would be well served to study his piece.