What does the principal investigative arm of the U.S. Department of Justice aka the F.B.I. do? How does the Federal Bureau of Investigation or FBI protect the American people & uphold the constitution of the United States?

The links below are relevant to the FBI & its role in protecting the American people:

https://scientificorigin.com/what-exactly-does-the-fbi-do-a-detailed-overview-of-the-fbis-roles-and-functions#google_vignette

https://www.fbi.gov/

https://www.fbi.gov/about/mission

https://www.fbi.gov/about/leadership-and-structure

https://www.fbi.gov/history

https://www.justice.gov/doj/federal-bureau-investigation