72 Congressman File Amicus Brief in Suit against Illegal Wiretapping
The administration, not to be outdone, had already moved on to surveillance of millions of American citizens not suspected of illegal activity. This revelation matches nicely with previous information about the NSA building secret rooms in telephone switching stations. By tapping into the phone network at this level, the NSA could trace most, if not all, calls within the United States.
This gives them information that could easily be used for blackmail (people calling mistresses), to identify who calls different press sources, could allow anonymous tipsters for the police to be identified, and to identify networks of activists. Since the NSA shares information it gathers with other intelligence services, it's possible that other nations are receiving surveillance on Americans who are dissidents fleeing from oppression in that same nation.
This program sounds not very different from one called Project Shamrock, in which the NSA surveilled all telegraphic communications without any explicit authorization, just an informal agreement with the telegraph companies. The revelation of that program, along with watchlist searches targeting American citizens for warrantless surveillance, was a major impetus for the creation of FISA.
Senator Roberts indicated that he was probably briefed on this illegal surveillance but said nothing.