The FBI in "uncharted" territory, never legally chartered by Congress ..

For starters, the FBI hardly belongs in the same set with concepts like “constitutional” or “ rule of law.” That’s because the FBI was never established by a law. US Lawmakers refused to approve an FBI bureau over a century ago when it was first proposed by Teddy Roosevelt. So he ignored Congress, and went ahead and set it up by presidential fiat. That’s one thing the civil liberties crowd hates discussing — how centralized US political power is in the executive branch, a feature in the constitutional system put there by the holy Founders.

https://www.nakedcapitalism.com/2017/05/mark-ames-fbi-no-legal-charter-lots-kompromat.html

First, the FBI mandate must scrupulously avoid inviting First Amendment violations; it should, for instance, discourage FBI interference in political dissent. Second, the charter should remove any lingering concern about inherent presidential power in regard to the bureau; congressional oversight would ensure that the FBI is not viewed as a tool of the president. Moreover, the charter should provide for an independent audit of FBI activities; currently the Justice Department both supervises and audits the agency.

https://www.csmonitor.com/1980/0611/061116.html