The 0bama administration so thoroughly abused the IG statute, that Horowitz for years pushed for a new, stronger law. He finally got 0bama to sign one, in the lame duck session after Trump was elected [12/21/16].
That timing is interesting, and suspicious. One wonders if 0bama would have signed the tougher law had his gal won...
Up until that time, DOJ and a number of other cabinet offices used some ambiguity in the old law to claim that the IG could not investigate them. This is one of the reasons there was no one except Congress complaining about Fast and Furious.
Now, here is where it gets interesting.
Sally Yates, the Deputy AG who was later fired by Donald Trump, issued a DOJ finding that even the new IG law could not be applied to the Department of Justice National Security Division, and by extension to the FBI Counter Intelligence which falls under their direction.
Those parts of the DOJ are precisely the ones containing ALL of the bad actors associated with the Steele Dossier. The question is, during the time that the IG was running his investigation, was Yates finding still in force, or did Sessions get someone to issue a new finding, which would have allowed Horowitz to investigate the worst parts of the DOJ/FBI?
I don't believe the answer to this question is currently known.