Congress has decided to take a long-overdue look at the administration's use of drones and has uncovered some startlingly loose rules.

NBC News recently acquired a memo that the administration provided the Senate authorizing use of aerial drone strikes against U.S. citizens abroad. It justified the 2011 killing in Yemen, by a drone strike, of three American citizens - Anwar al-Awlaki, his son Abdulrahmen al-Awlaki and Samir Khan.

Whereas the targets were specific, the memo's justification for the strike was not.

It argued that a citizen engaged in terrorism who could not be captured may be killed under the law if "an informed, high-level official" of the government decided that the target was an al-Qaida figure who could be the source of "an imminent threat of violent attack against the United States."

That sounds reasonable and most citizens aren't going to shed any tears for those engaged in terrorism against the United States.

But the memo does not define what constitutes proof of an imminent threat of violent attack. Nor does it even define which "informed, high-level official" may pull the trigger on an American citizen without charges, much less a trial.

Clearly, a president must have the authority to act. But that is not mutually exclusive from the rule of law, the nation's guiding principle. This controversy isn't a simple case of squeamishness over drone strikes; it's about fundamental principles.

As written, the memo simply would allow any president, or perhaps someone else, pull the trigger based purely on suspicion and define the scope of the threat later.

Congress should insist that the administration tighten its rules in a way that also defends the nation's principles.