The State Department has emphasized that one of the major standards for the use of lethal force is that the threat to the United States must be “imminent.” The rationale behind the standard is well grounded in international law.
However, the State Department and the CIA have adopted a doctrine in determining whether a threat is imminent which undermines—and perhaps eliminates entirely—the requirement that the threatened harm be “imminent,” as judged by a reasonable person. This is the so-called “doctrine of last opportunity.” Under this doctrine, even if a threat is not imminent in the normal sense of the term, the standard of imminence can still be satisfied if the decision-maker believes this is the last opportunity that the US is likely to have to target the individual or individuals. As it is difficult to track likely subjects for a targeted kill, and as the targets go to great lengths to avoid detection by the US, it is possible that the window of last opportunity standard would be met in most circumstances, thereby, effectively eliminating the requirement for imminence of the threat to the US.
The Justice Department legal memo outlined its own definition of “imminence,” which it considers the first condition to be met for a lawfully justified lethal targeting of an American citizen. Providing further clarification for that word, “the condition that an operational leader present an ‘imminent’ threat of violent attack against the United States does not require the United States to have clear evidence that a specific attack on U.S. persons and interests will take place in the immediate future.”
The paper memo continues—
“Delaying action against individuals continually planning to kill Americans until some theoretical end stage of the planning for a particular plot would create an unacceptably high risk that the action would fail and that American casualties would result.
“By its nature, therefore, the threat posed by al-Qa’ida and its associated forces demands a broader concept of imminence in judging when a person continually planning terror attacks presents an imminent threat, making the use of force appropriate. In this context, imminence must incorporate considerations of the relevant window of opportunity, the possibility of reducing collateral damage to civilians, and the likelihood of heading off future disastrous attacks on Americans.”
This reasoning seems to put few practical boundaries on who and what poses an imminent threat to the United States.