the FBI. Steele became frustrated with the FBI, for sitting on the information that he provided, so he took his work public (the FBI "cabal" was covering up for trump, while digging for dirt on clinton.)
Grassley's "investigation" is the biggest nothingburger of the all. Steele is a British citizen and an independent contractor (in this case). What jurisdiction would Grassley/trump's doj have over him? Did Steele come to the US, or were transactions handled electronically (with him on sovereign soil)?
This is all just a smoke screen - the last thing team trump would want is for Steele to take a witness stand.
http://www.independent.co.uk/news/world/americas/donald-trump-russia-dossier-file-investigation-hacking-christopher-steele-mi6-a7526901.html