After Watergate, Congress exposed how the F.B.I. had surveilled, blackmailed and intimidated activists, celebrities and politicians. To prevent such abuse, President Gerald Ford’s administration prohibited the agency from opening investigations without reasonable suspicion of a crime. In 2008, Attorney General Michael Mukasey and his Justice Department worked around that reform by creating a new category of F.B.I. investigations called “assessments.” Under the new policy, agents could use physical surveillance and interview acquaintances, as well as informants, to gather information, even in the absence of a demonstrably high level of suspicion.