NBC News has obtained an official White House memo, which lays out the legal justification behind using drones for the targeted killing of American citizens abroad. Three Americans have been killed via a drone strike under the Obama Administration, including Anwar al-Awlaki, his son, and Samir Khan.

According to the document, President Obama, and other high-level administration officials, can order the killing of an American overseas if the individual is an imminent threat, incapable of being captured, and the operation is compatible with the rules of war. As far as what constitutes an “imminent threat,” the document provides an overly broad definition, arguing that even if the individual is not actively engaged in an imminent attack against America, he or she can still be considered an “imminent threat”, if they have in the past plotted to attack Americans, and remain a member of a hostile organization.

It’s doubtful this sort of legal justification could hold up to judicial scrutiny, and civil liberties groups are up in arms after the leak. Hina Shamsi, the director of the ACLU’s National Security Project, said the White House’s justification for targeted killings, “Summarizes in cold legal terms a stunning overreach of executive authority –- the claimed power to declare Americans a threat and kill them far from a recognized battlefield, and without any judicial involvement before or after the fact…hard to believe it was produced in a democracy built on a system of checks and balances.”

The man who crafted the White House’s drone policy is top adviser John Brennan. And he’s also President Obama’s nominee to head up the CIA, meaning it’s unlikely the President is having second thoughts about the drone warfare program, which has been ramped up during his presidency.

This will be the greatest national security challenge facing our nation in the coming years. We must stop the senseless robotic killings abroad, and bring back the rule of law in America.