https://www.techdirt.com/articles/20191008/17514543157/fisa-court-finds-fbi-is-still-violating-fourth-amendment-with-abuse-nsa-collections.shtml

The NSA isn't the only agency to abuse its surveillance powers. The FBI's ability to access unminimized data harvested by the NSA has resulted in abuse after abuse, as the FBI loves to use the massive data haul to perform "backdoor searches" of its domestic targets.

This concern has been raised repeatedly, most notably by Sen. Ron Wyden, who has been calling out surveillance abuses for years -- specifically calling out these backdoor searches and hinting (strongly) that they are much more prevalent than most people believed. Nothing much has been done about it, other than multiple federal agencies suggesting they too should be put on the ever-growing list of entities with access to the NSA's multiple collections.