The paper obtained by NBC was apparently meant to be used to brief members of Congress. It outlines a three-part test for when US citizens might end up in their own nation’s cross-hairs.
First, they must be senior members of Al Qaeda. Second, they must pose an imminent threat of violent attack against the US. Third, it must be infeasible for US or allied forces to capture the individual in question.
All that’s required, under the memo’s wording, is for a well-informed top official of the US government to decide that the person in question is a top terrorist. As for “imminent,” that does not mean “about to happen” in this case. It means only that the alleged terrorist must have recently been involved in activities posing a threat of violent attack and that there is no evidence they’ve renounced those activities.