The use of the nuclear bomb in World War II fundamentally altered the nature of modern warfare. For the United States, it forever changed the role of the presidency, giving the executive branch the power to unilaterally detonate a stunningly destructive bomb. Today, drones have, arguably, become the modern version of the nuclear bomb, controlled from a computer, with the potential for no loss of American life, no boots on the ground, and a relatively small price tag.   The use and deployment of drones rests comfortably in the hands of the president. He alone can order the killing of another human being abroad, including an American citizen. To date, three Americans have been killed in Yemen in drone strikes, include Anwar al-Awlaki, the leader of Al Qaeda in the Arabian Peninsula. It's a presidential power that Attorney General Eric Holder has reaffirmed in the face of imminent danger.   David Cole, professor of constitutional law, national security, and criminal justice at Georgetown University Law Center, says that the administration legally justifies the drone program with two legal documents: First, they can engage in targeted killing on the battlefields of Afghanistan and Pakistan because it's a war. And second, the targeted killings in Yemen and Lebanon – thousands of miles away from any battlefield – are justified because those individuals they are targeting are an imminent threat. According to Cole, "They have redefined imminence to say that if somebody is involved in one of these groups that's associated with Al Qaeda and they're an operational leader, then by definition they constantly pose an imminent threat to us." "In this program, a judge doesn't decide anything," he says, "because the administration has taken this authority on for itself and asserts that it doesn't have to get any approval from any other branch, whether it be Congress or the judiciary, to kill even an American citizen."