Lawmakers voiced their confusion and concern, and some called for the end of sweeping surveillance programs by US spy agencies after receiving an unusual briefing on the government's yearslong collection of phone records and Internet usage.
The phalanx of FBI, legal and intelligence officials who briefed the entire House was the latest attempt to soothe outrage over National Security Agency programs that collect billions of Americans' phone and Internet records. Since they were revealed last week, the programs have spurred distrust in the Obama administration from around the world.
Congressional leaders and intelligence committee members have been routinely briefed about the spy programs, officials said, and Congress has at least twice renewed laws approving them. But the disclosure of their sheer scope stunned some lawmakers, shocked foreign allies from nations with strict privacy protections and emboldened civil liberties advocates who long have accused the government of being too invasive in the name of national security.
Some congressmen admitted they'd been caught unawares by the scope of the programs, having skipped previous briefings by the intelligence committees.
"I think Congress has really found itself a little bit asleep at the wheel," Democratic Rep. Steve Cohen of Tennessee said.
Many leaving the briefing declared themselves disturbed by what they'd heard - and in need of more answers.
"Congress needs to debate this issue and determine what tools we give to our intelligence community to protect us from a terrorist attack," said Rep. CA Dutch Ruppersberger of Maryland, top Democrat on the House Intelligence Committee, and a backer of the surveillance.
"Really it's a debate between public safety, how far we go with public safety and protecting us from terrorist attacks versus how far we go on the other side."
He said his panel and the House Judiciary Committee will examine what has happened and see whether there are recommendations to be made for the future.
The Senate Appropriations defense subcommittee will get to question the head of the NSA, Gen. Keith Alexander, on Wednesday, and the Senate and House intelligence committees will be briefed on the programs again Thursday.
The country's main civil liberties organization wasn't buying the administration's explanations, filing the most significant lawsuit against the massive phone record collection program so far. The American Civil Liberties Union and its New York chapter sued the federal government Tuesday in New York, asking a court to demand that the Obama administration end the program and purge the records it has collected.
The ACLU is claiming standing as a customer of Verizon, which was identified last week as the phone company the government had ordered to turn over daily records of calls made by all its customers.
Polls of U.S. public opinion show a mixed response to the controversy. A poll by The Washington Post and the Pew Research Center conducted over the weekend found Americans generally prioritize the government's need to investigate terrorist threats over the need to protect personal privacy.
But a CBS News poll conducted June 9-10 showed that while most approve of government collection of phone records of Americans suspected of terrorist activity and Internet activities of foreigners, a majority disapproved of federal agencies collecting the phone records of ordinary Americans.
Thirty percent agreed with the government's assessment that the revelation of the programs would hurt the US' ability to prevent future terrorist attacks, while 57 percent said it would have no impact.
On Capitol Hill, the ire was unanimously focused on Edward Snowden, the CIA employee-turned-NSA contractor who admitted in interviews with two newspapers that he exposed the programs in an attempt to safeguard American privacy rights from government snooping.
House Speaker John Boehner called the elusive, 29-year-old former intelligence contractor a "traitor."
Senate Intelligence Committee Chairwoman Dianne Feinstein also called the disclosure "an act of treason" and said Snowden should be prosecuted.
A law enforcement official said prosecutors were building a case against Snowden on Tuesday and had not decided what charges would be brought against him.
US officials have said Snowden would have had to sign a nondisclosure agreement to handle the classified material and at the least could be prosecuted for violating it.
But it was unlikely Snowden would be charged with treason, which carries the death penalty as a punishment and therefore could complicate extradition from foreign countries.
The official spoke on condition of anonymity because there had been no final decision on the charges.
Snowden, who was fired Tuesday from his job with government contracting firm Booz Allen Hamilton, was last seen in Hong Kong. His whereabouts were unknown Tuesday.