Under President George W. Bush, the limits on targeted killing were clear, initially. In 2002, the president had to give the CIA special authority to target senior Iraqi commanders in the run-up to war. After the Iraqi surrender, many of the notorious “deck of cards” leaders were captured, not killed — including Saddam Hussein himself.

Drones changed the balance. They provided a new technology of retribution and became an almost addictive way of using lethal force without risking U.S. casualties. Drones do not capture; they kill. That’s why it’s so important to have clear rules.

Holder was so determined to keep presidential options open that he gave a vague answer to Paul’s question about targeting U.S. citizens on American soil. “It is possible, I suppose, to imagine an extraordinary circumstance in which it would be necessary and appropriate,” he said — conjuring up another Pearl Harbor or 9/11 when the suicide attackers were Americans. That answer worried millions of other Americans who fear abuse of government power. …

These questions are urgent, as al-Qaeda morphs into smaller spinoffs and the legal justification for attacks becomes more tenuous. The Post reported this week that, to attack al-Qaeda offshoots in such places as Syria, Libya and Mali, the United States might expand targeting to what a source called “associates of associates.”