While Mr. Obama surely does not seek a return to these earlier forms of conflict, a return to first principles such as hostis humani generis may prove a better guide for a nation at war than a president's day-to-day instincts.

WSJ: John Yoo: Obama, Drones and Thomas Aquinas

The work of the Catholic theologians drew upon traditions stretching back to the ancient world that would have considered terrorists to be hostis humani generis, the enemy of all mankind, who merited virtually no protections under the laws of war.

WSJ: John Yoo: Obama, Drones and Thomas Aquinas