So what Trump and Pompeo seem to be describing is a preventive military strike, not a preemptive strike.
The distinction between the two is crucial. Under international law, a “preemptive” military action to thwart an imminent threat is generally viewed as an acceptable act of self-defense.
“Preventive” military action, taken in response to less immediate threats, is not.
Our enemies around the world are plotting against American interests all the time. That’s why we call them enemies. If that alone were enough to justify taking military action against them without congressional authorization, there would be no limit on a president’s unilateral use of military force.
Does North Korea pose an imminent threat? Russia? China? Syria? Should President Trump—or, if you prefer, the next Democratic president—be free to launch attacks against any of them without a declaration of war or specific congressional authorization?