The Obama administration calls it "targeted killing." Steven Seagal would call it getting marked for death. It's the practice of singling out an individual, linked to a terrorist group, for killing, and it's been played out hundreds of times in the 9/11 era – including, more recently, against U.S. citizens like al-Qaida's YouTube preacher, Anwar al-Awlaki. The Obama team has said next to nothing about how it works or what laws restrict it. Until Monday.

Attorney General Eric Holder explained the administration's reasoning for killing American citizens overseas – and only overseas – with drone strikes and other means during a Monday speech at Northwestern University. Holder claimed that the government can kill "a U.S. citizen who is a senior operational leader of al-Qaida or associated forces" provided the government – unilaterally – determines that citizen poses "an imminent threat of violent attack"; he can't be captured; and "law of war principles," like the use of proportional force and the minimization of collateral damage, apply.

"This is an indicator of our times," Holder argued, "not a departure from our laws and our values."

The debate over killing Awlaki, whom Holder barely discussed, began long before a Hellfire missile fired from a drone killed him and fellow propagandist Samir Khan in September. Awlaki's father sued the Obama administration in 2010 to compel it to reveal its legal rationale for the long-telegraphed strike. (Full disclosure: My wife works for the ACLU, which helped Nasser al-Awlaki with his lawsuit.) The administration refused, with a judge's support.

For months after Awlaki's killing, the government never disclosed any evidence supporting its decision that Awlaki posed an imminent danger to Americans, beyond his rhetoric of incitement. But during the February sentencing of the "Underwear Bomber," the government put forward a court filing claiming that Awlaki worked intimately with convicted would-be bomber Umar Farouk Abdulmutallab to blow up Northwest Airlines Flight 253. Holder referred to that connection in his speech.

Several legal scholars have wondered why the U.S. didn't have to provide Awlaki with due process of law before killing him, as stipulated under the Fifth Amendment. Holder contended that the U.S. actually did – even if no judge ever heard Awlaki's case.

"The Constitution's guarantee of due process is ironclad, and it is essential – but, as a recent court decision makes clear," Holder argued, "it does not require judicial approval before the president may use force abroad against a senior operational leader of a foreign terrorist organization with which the United States is at war – even if that individual happens to be a U.S. citizen."

Holder left several aspects of his argument unexplained. He did not define the terms "senior operational leader" of al-Qaida, nor what it means to be an "affiliate" of the amorphous group. The attorney general only referred to the drones through the euphemism "stealth or technologically advanced weapons." Holder did not explain why U.S. forces could not have captured Awlaki instead of killing him, nor what its criteria are for determining on future missions that suspected U.S. citizen terrorists must be killed, rather than captured. Holder did not explain why Awlaki's 16-year-old son, whom a missile strike killed two weeks after his father's death, was a lawful target. Holder did not explain how a missile strike represents due process, or what the standards for due process the government must meet when killing a U.S. citizen abroad. Holder did not explain why the government can only target U.S. citizens suspected of terrorism for death overseas and not domestically.

The decision to kill an American, Holder said, is "among the gravest that government leaders can face." Targeted killing is not assassination, he argued, because "assassinations are unlawful killings." Among the few external limitations on the government's war power that Holder mentioned were the approval of a local government where the strikes occur – which must have pleased reluctant, unsteady U.S. allies in Pakistan and Yemen – and the after-the-fact disclosure of the strikes to Congress.

Some members of Congress do not consider that a sufficient safeguard.

"The government should explain exactly how much evidence the president needs in order to decide that a particular American is part of a terrorist group," says Sen. Ron Wyden, an Oregon Democrat who sits on the Senate's intelligence committee. "It is also unclear to me whether individual Americans must be given the opportunity to surrender before lethal force is used against them. And I'm particularly concerned that the geographic boundaries of this authority have not been clearly laid out. And based on what I've heard so far, I can't tell whether or not the Justice Department's legal arguments would allow the President to order intelligence agencies to kill an American inside the United States."

Mary Ellen O'Connell, the vice president of the American Society of International Law, found Holder's legal rationale flimsy.

"First, [Holder] restates the renamed global war on terror, which Obama himself condemned. Then he tries the United Nations Charter Article 51 but does not include the whole article: It says member states of the U.N. have an 'inherent right of self-defense' if an armed attack occurs. Article 51 does not provide a legal green light for targeted killing," O'Connell said in an e-mail. "Finally, he adds the argument that the U.S. may use force against states that are 'unable or unwilling' to act. This argument has no basis in international law. It simply does not exist. So regardless of how carefully you target under the law of armed conflict, there is no right in the first instance to target at all."

Holder's speech signaled that there are other Americans whom the government is considering killing like it killed Awlaki. The Somali terror group al-Shabab, which recently merged with al-Qaida, has an American adherent named Omar Hammami. The central al-Qaida organization boasts an English-speaking propagandist named Adam Gadahn, a Californian.

Similarly, the Obama administration has elevated stealthy, global "shadow wars" to a central aspect of its national-security strategy. Those wars, usually prosecuted through drones or elite special operations forces, have proliferated far from the declared battlefields of Afghanistan and Iraq, to Pakistan, Yemen, and East Africa. The administration has not explained how they will come to a successful conclusion.

"In the continuing effort to keep our people secure, this administration will remain true to those values that inspired our nation's founding and, over the course of two centuries, have made America an example of strength and a beacon of justice for all the world," Holder said. "This is our pledge."