FISA was passed in the wake of the
Keith case, formally
United States v. U.S. District Court, 407 U.S. 297 (1972)
The underlying event was bombing of a CIA office. The fact that the government had conducted surveillance without a warrant complicated the government's case.
Within this opinion are a few items worth noting. Two in particular:
- SCOTUS suggested Congress create a FISA court
- The fourth amendment is not violated if the government snoops without a warrant, for foreign intelligence purposes
Since FISA was passed in 1978, no FISA warrant has even been used in a criminal case. The entire FISA system is make-work for the purpose of fooling the public into believing snooping is effectively regulated by court oversight.
FISA creates a crime for activity SCOTUS views as a constitutional prerogative of the president. There is a good argument that the statute is unconstitutional because it criminalizes constitutionally-protected conduct.