Efforts to rein in the once-secret surveillance programs have attracted an unusual coalition of liberal Democrats and libertarian Republicans, pitting them against House and Senate leaders who have expressed strong support for the NSA programs.
Four senators unveiled legislation earlier this week to end the collection of millions of Americans' phone records and data on Internet usage. The legislation by three Democrats and one Republican would end longstanding NSA surveillance practices and open up some of the actions of the FISA court, the secret federal court that reviews government surveillance requests.
Sen. Dianne Feinstein, D-Calif., the intelligence committee chairwoman, has defended the bulk collection of data. She said her committee is drafting legislation to broaden the government's ability to electronically monitor terror suspects who travel to the U.S. if they were already under surveillance overseas by the NSA.
Feinstein said the bill would change the part of the law that allows targeting non-Americans outside the U.S. to allow uninterrupted spying on a suspect for "a limited period of time after the NSA learns the target has traveled to the United States, so the government may obtain a court order based on probable cause."
The proposal is intended to close what lawmakers describe as a brief surveillance gap that occasionally can occur because of varying legal standards between the NSA's operations, directed principally overseas, and the FBI's traditional role of tracking suspects on U.S. soil.
NSA commander Gen. Keith Alexander, one of the witnesses at Thursday's hearing, testified previously there is no evidence of intentional wrongdoing in any of the NSA spying programs, even though the agency has reported thousands of errors to the FISA court. Intelligence officials blame those errors on a system so complex that no single person at the NSA understood it.
In a declassified internal report from 2012, NSA said nearly three-quarters of the 2,776 compliance incidents where NSA analysts made surveillance errors involved suspects who had been under surveillance abroad before entering the U.S. legally, or illegally.
The NSA's mandate forbids it from spying on anyone inside the U.S., except in rare court-approved instances.
In most cases, it falls to the FBI to track such suspects — and when the NSA calls to report a so-called "roamer," it already has stopped surveillance.
The FBI then has to decide quickly if the person is dangerous enough to start following electronically, and if so, scrambles to build a case against the suspect. The FBI can ask the attorney general for emergency authority to track the target for seven days but then must win retroactive approval for the spying from the FISA court.
"I call it the terrorist lottery loophole," where surveillance can be dropped for a matter of hours or days during the handoff between agencies, said Rep. Mike Rogers, R-Mich., chairman of the House Intelligence Committee, who also supports changing the law.
"Bottom line is, there is a gap," said the senior Democrat on the committee, Rep. C.A. Dutch Ruppersberger, D-Md.
"If in that gap period ... there's an attack that kills Americans ... shame on us all."