On Tuesday, during a House Judiciary Committee hearing, we got a lot closer to proof, thanks to Deputy Attorney General James Cole. As reported in National Journal:

Rep. Zoe Lofgren, a California Democrat, began by asking Peter Swire, a member of the president's handpicked surveillance review board, whether lawmakers' numbers are included in the agency's phone-records sweeps. Swire protested that he was not a government official and couldn't best answer the question, but said he was unaware of any mechanism that "scrubbed out" member phone numbers from the agency's data haul. Lofgren's time expired and Rep. Darrell Issa, a California Republican, then put the question to Cole. "Mr. Cole, do you collect 202, 225, and four digits afterwards?" Issa asked, referring to the prefixes used to call congressional offices. "We probably do, Mr. Congressman," Cole responded. "But we're not allowed to look at any of those, however, unless we have reasonable, articulable suspicion that those numbers are related to a known terrorist threat."

These are alarming answers for several reasons.

1) Most importantly, this is an obvious threat to our democracy and the separation of powers upon which it relies. It gives the executive branch, under this president and all future presidents, a powerful, illegitimate means to undermine legislative opponents. In fact, legislators could be targeted in a way that would be both devastating and easy to pull off without even the victim knowing what happened. There's no need to blackmail. Just dig up some dirt on a legislator, or his spouse, or her business partner, using metadata; figure out how an opposition researcher might happen upon the same information; and leak it to the press as if you are one. The executive branch is already becoming expert at parallel construction. It's perhaps easier than breaking into the Watergate.

NSA defenders insist that the professionals at that agency would never stand for such abuses, that they are just there to protect the safety of Americans. If that retort is offered in earnest, it only proves that those using it don't understand the precautions that must be taken in order to insure against abuses by fallible humans. The U.S. soldiers who perpetrated the horrors at Abu Ghraib mostly enlisted to protect their country. The FBI agents who tried to blackmail Martin Luther King mostly signed up for their jobs to protect their country. The folks who carried out the Watergate break-in mostly joined the Nixon Administration with at least some altruistic motives. But power often corrupts judgment and character.

That aspect of human nature will never change. Abuse attempts will happen in the future, including at the NSA. The damage done will depend in part on how much power is concentrated there. The dragnet concentrates lots of power over legislators and other Americans in a secretive agency with a history of repeated legal abuses; an agency staffed with employees who carried out illegal, warrantless wiretapping under the last president; an agency that could easily poke around in the metadata without its overseers knowing if it wanted to abuse its power again.