There’s a great (but long) article at CTH that explains the importance to the un-elected cabal (aka invisible government) of controlling the FBI.
Other than the obvious favoritism of RATS and persecution of MAGA, the FBI is in charge of all security clearances.
This gives them the power, over time, to fully populate almost every agency with their puppets.
Many of President Trump’s nominees were blocked in this fashion; but this has been going on a long time.
The article also pinpoints a key victory of the invisible government in setting up “Intelligence agencies” as a 4th branch of government was the Patriot Act ... orchestrated largely by Dick Cheney in the aftermath of a certain VERY LARGE FALSE FLAG.
Defense Security Services (DSS) does defense related ones.