In practice, then, the White House seems to believe that a U.S. citizen who is high up in al-Qaeda, or an affiliate, has signed his own death warrant. (Although the paper doesn’t address the question, it implies that non-citizens wouldn’t even need to be high up to be killed.)

To support its argument that it has the legal authority to kill citizens, the administration has cited the Authorization for Use of Military Force, which Congress passed three days after the attacks of Sept. 11. That legislation gives the president the power “to use all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001, or harbored such organizations or persons, in order to prevent any future acts of international terrorism against the United States by such nations, organizations or persons.”

It isn’t clear that this justification goes as far as the administration maintains. More than 11 years after the attacks, an al-Qaeda affiliate could be led by someone with no real complicity in them. It would be a stretch to say the 2001 law justifies taking action against such a person whether he is a citizen or not. The white paper’s secondary justification — the president’s “constitutional responsibility to protect the country” — doesn’t fill the gap. That responsibility requires the president to act, even in the absence of congressional authorization, against someone planning a specific attack on America. The white paper has more amorphous threats in mind.