WASHINGTON -- Sen. Dianne Feinstein (D-Calif.), a staunch defender of government surveillance of ordinary citizens, took to the Senate floor Tuesday with the stunning accusation that the Central Intelligence Agency may have violated federal law to spy on Congress.

Feinstein, head of the Senate Intelligence Committee, railed against the CIA for compromising the legislative branch's oversight role -- a theme echoed by many of her Senate colleagues throughout the day. The outrage was palpable among lawmakers on both sides of the aisle, and some suggested CIA Director John Brennan should resign if the allegations are true. Sen. Lindsey Graham (R-S.C.), who has stuck up for intelligence agencies in the past, declared a potential war.

"This is Richard Nixon stuff," Graham told reporters. "This is dangerous to the democracy. Heads should roll, people should go to jail if it’s true. If it is, the legislative branch should declare war on the CIA."

When former contractor Edward Snowden revealed last year that the National Security Agency was secretly collecting phone and electronic records from millions of ordinary Americans, the response in Congress was far more muted. Top senators insisted the surveillance was critical to U.S. counterterrorism activities.

"It's called protecting America," Feinstein said then. Graham said he was glad Verizon was turning over customer records to the government to ensure that his phone was not linked to any terrorist activity.

It was not until reports that the NSA had spied on foreign leaders and allies, such as German Chancellor Angela Merkel, that Feinstein offered criticism of the agency's surveillance.

Snowden said Tuesday it was hypocritical for some lawmakers to finally express anger when the privacy of elected officials was breached.

"It’s clear the CIA was trying to play 'keep away' with documents relevant to an investigation by their overseers in Congress, and that’s a serious constitutional concern," Snowden said in a statement to NBC News. "But it’s equally if not more concerning that we’re seeing another 'Merkel Effect,' where an elected official does not care at all that the rights of millions of ordinary citizens are violated by our spies, but suddenly it’s a scandal when a politician finds out the same thing happens to them."

Libertarians and liberals in Congress were the NSA's primary critics throughout 2013, trying repeatedly -- and unsuccessfully -- to curb some of the bulk data collection programs. That same bloc of lawmakers argued Tuesday that whether it was citizens or Congress being spied on, both were worthy of condemnation.

"It's outrageous when this happens to Congress, and it's outrageous when this happens to the American people," Sen. Mike Lee (R-Utah) told The Huffington Post.

Lee added that the CIA's alleged actions may give lawmakers a better understanding of what it feels like to be secretly surveilled.

"I think when it happens to them, it certainly demonstrates that this is more than just a hypothetical concern," Lee said. "It helps bring the issue home, it helps bring the issue into perspective."

Sen. Mark Udall (D-Colo.), another vocal critic of the NSA, told HuffPost it was important to uphold the public's trust "at every juncture." His constituents already shared "broad concern" about the NSA's metadata program and would now be "deeply concerned" about the CIA spying on the body designated with oversight of the federal government's executive branch.

"Over time, I believe my point of view, which is that we ought to be outraged about both situations, has begun to take hold," Udall said.

Sen. Richard Blumenthal (D-Conn.) has been a leading advocate for reforming the Foreign Intelligence Surveillance Court, which authorizes some of the NSA surveillance programs. If the CIA spied on Congress, it would raise legal questions that may get a great deal of scrutiny, he said.

"There's the additional constitutional considerations involving two separate branches of government, one taking illegal action against another," Blumenthal told HuffPost. "The constitutional ramifications elevate the issue to a higher level."