Later this afternoon, John Brennan, President Obama's chief counterterrorism strategist will be questioned by a Congressional intelligence committee for a shot at becoming the next director of the CIA. But more than being mere procedure, the hearing has the potential to draw back the curtain ever-so-slightly on one of the Obama administration's most secretive and controversial policies: the use of unmanned aerial drones to remotely assassinate terror suspects — including American citizens located overseas — without oversight or due process.

Following the leak of a confidential memo detailing the administration's elastic legal justifications for drone strikes that kill American citizens, the President has granted members of Congressional intelligence committees — but not the public — access to classified documents which supposedly justify the killing of Anwar al-Awlawki and his 16-year old son, Abdulrahman — two of the four US citizens killed by drones overseas in 2011.

Lawmakers have a rare opportunity to question the deadly practices

The timing was no accident: the order came a few days after 11 Senators wrote to the President demanding the administration's criteria for targeted killings. It was also just ahead of today's confirmation hearing for Brennan, the 25-year CIA veteran vying for the agency's top spot. Senator Ron Wyden (D-Ore.), who said he would "pull out all the stops" to get answers during the hearing, told MSNBC this morning that the President's decision was "an encouraging one, but there’s certainly a lot more to do.” More importantly, it means lawmakers have a rare opportunity to question the deadly practices that until recently administration officials have refused to discuss or even acknowledge publicly.

It's been a long time coming. According to the Bureau of Investigative Journalism, drone strikes have reportedly killed between 2,562 and 3,325 people, a significant number of them civilians including children, in non-combat zones throughout Pakistan's designated tribal areas since 2004, with even more reported in Yemen and Somalia. (A more conservative estimate from the New America Foundation puts the number between 1,953 and 3,279, with a sharp decrease in the percentage of civilian casualties since 2006.) They are carried out in secret using a "kill list" available only to the President and his closest aides, including Brennan, who has been at the helm of the program since 2008.

The administration has never acknowledged the CIA program officially

Neither Brennan nor the rest of the administration have ever acknowledged the CIA program officially, but reports citing unnamed sources within have repeatedly referenced it. What few details have been deciphered point to an incredibly broad campaign: according to reports from the New York Times and others, the administration considers all men of military age killed in stikes to be "militants," has engaged in so-called "signature strikes" that kill unidentified individuals based on "supicious behavior," and employs something called the "double tap" — a follow-up strike that targets first responders arriving at the scene, which is regarded by the United States itself as a terrorist tactic.

The leaked DOJ memo, obtained by NBC News on Monday, gave some hint into the thinking behind the administration's use of lethal strikes. It cites the Authorization for the Use of Military Force (AUMF) that was signed into law shortly after 9/11 as its primary qualifier, and specifies "senior Al Qaeda members" and "associated forces" that represent an "imminent threat of violent attack" against the United States as its legitimate targets. But it also claims a broader definition of "imminent" which does not require that the US government have any evidence whatsoever of a specific attack in the near future, thus reducing the word's meaning to effectively nil.

The administration's posturing on the issue has evolved significantly as new facts come to light. Recently, Brennan himself has defended the strikes, arguing that they are "consistent with the inherent right of self-defense." And while it's unlikely that any criticism from the Senate Intelligence committee will derail his confirmation, Brennan does face a lot of difficult questions in today's hearing about the civilian impact of drone strikes, the justifications behind them, and limits of government secrecy — questions that members of Congress may not have the opportunity to ask again publicly in the foreseeable future.

The hearing is streaming live on C-SPAN starting at 2:30 PM EST