An existential fight over the US government’s ability to spy on its own citizens is brewing in Congress. And as this fight unfolds, the Federal Bureau of Investigation’s biggest foes on Capitol Hill are no longer reformers merely interested in reining in its authority. Many lawmakers, elevated to new heights of power by the recent election, are working to dramatically curtail the methods by which the FBI investigates crime.

New details about the FBI’s failures to comply with restrictions on the use of foreign intelligence for domestic crimes have emerged at a perilous time for the US intelligence community. Section 702 of the Foreign Intelligence Surveillance Act (FISA), the so-called crown jewel of US intelligence, grants the government the ability to intercept the electronic communications of overseas targets who are unprotected by the Fourth Amendment.

That authority is set to expire at the end of the year. But errors in the FBI’s secondary use of the data—the investigation of crimes on US soil—are likely to inflame an already fierce debate over whether law enforcement agents can be trusted with such an invasive tool.