However, that apparent perfect rationality criticism is countered and so is consistent with current deterrence policy. In "Essentials of Post-Cold War Deterrence", the authors detail an explicit advocation of ambiguity regarding "what is permitted" for other nations and its endorsement of "irrationality" or, more precisely, the perception thereof as an important tool in deterrence and foreign policy. The document claims that the capacity of the United States, in exercising deterrence, would be hurt by portraying US leaders as fully rational and cool-headed: