"[T]he Office recognized that its investigation could identify foreign intelligence and counterintelligence information relevant to the FBI's broader national security mission. FBI personnel who assisted the Office established procedures to identify and convey such information to the FBI. The FBI's Counterintelligence Division met with the Office regularly for that purpose... [T]he FBI also embedded personnel at the Office... to review the results of the investigation... [C]ommunications and other correspondence between the Office and the FBI contain information derived from the investigation, not all of which is contained in this Volume. This Volume is a summary. It contains... information necessary to account for... prosecution and declination decisions and to describe the investigation's main factual results."