Congressmen are already lining up to label the Boston Marathon bombing as yet another failure of the U.S. intelligence community. The head of America's 16 spy agencies has a response for the Capitol Hill critics: back off.

Director of National Intelligence James Clapper urged Americans today "not to hyperventilate for a while before we get all the facts." In his most substantial public comments on the Boston attacks to date, provided at a suburban Washington intelligence conference, Clapper warned that finding the bombers in advance would require an invasion of Americans' privacy by the government that citizens would likely find intolerable.

"The rules were abided by, as best as I can tell at this point," he said at the confab, called the 12th Annual C4ISR Journal Conference. "The dots were connected."

Clapper and the spy community are facing questions about whether it was possible to detect suspected bombers and U.S. citizens Tamerlan and Dzhokhar Tsarnaev before the attack on April 15 that killed three people and wounded 180. While it appears the bombing was unconnected to any group or foreign actor – and hence hard to detect in advance – the FBI acknowledged it interviewed Tamerlan Tsarnaev in 2011 at the behest of a foreign intelligence agency, believed to be Russia, but "did not find any terrorism activity, domestic or foreign." At the CIA's request, his name went into a government database, known as the Terrorist Identities Datamart Environment, the Washington Post reported today, months after the FBI closed its inquiry. When Tamerlan Tsarnaev took a trip to Russia in January 2012, the Department of Homeland Security was "pinged" from a different database, the Treasury Enforcement and Communication System, but not upon his return to the U.S. six months later.

"The ball was dropped," Sen. Lindsey Graham said on CNN earlier this week. "We're at war with radical Islamists and we need to up our game."

Clapper cautioned that "just being in a database is not necessarily indicative of current nefarious behavior." The databases can include information on people who merely meet others whom the government considers suspicious; the criteria for inclusion on them is not public.

Members of Congress are starting to ask if the spy agencies couldn't have gone further to monitor the suspects. "Was that [travel] information shared in with the FBI and the Joint Terrorism Task Force?" asked Rep. Michael McCaul (R-Tex.), the chairman of the House Committee on Homeland Security, after Clapper spoke. "His departure from the U.S. would warrant a second look, I would think."

Clapper contended that detecting the bombers required giving the spy agencies even broader powers to monitor Americans' online activity. To what extent do Americans "want the government monitoring U.S. citizens' behavior, monitoring their social media," he asked, referencing to jihadist imagery posted on Tamerlan Tsarnaev's YouTube channel. "How intrusive do you want Big Brother to be?" It's worth mentioning, however, that the spy community has long monitored social media and online behavior.

Clapper also mused that it was "amusing and ironic" that some who tend to doubt Russia suddenly give credence to Russian warnings about the elder Tsarnaev. "You know, whenever the Russians say anything about arms control issues, we're very suspicious, you know, we're supposed to trust but verify, not accept what the Russians say," Clapper said. "But in this case we accept it, whatever they say, without question."

McCaul, in his later talk, pushed back against drawing the conclusion that the attacks weren't foreign sponsored, calling it "astounding" that "intelligence officials" are embracing it. "I reserve judgment until the evidence comes in," McCaul said. "They're scrubbing his computer right now."

Clapper is sure to face further questions from McCaul's colleagues in the coming weeks about Boston. "The bigger issue here," he contended, "is what is the government's responsibility to mind-read, and determine the point at which an individual might self-radicalize? In every testimony, virtually all the [intelligence] leadership has spoken to the difficulty of detecting the lone wolf, and it is a very tough problem."