The concept of such a machine is consistent with MAD doctrine when it is logically pursued to its conclusion. It thus worried Kahn that the military might like the idea of a doomsday machine and build one. Kahn, a leading critic of MAD and President Eisenhower's administration's doctrine of massive retaliation upon the slightest provocation by the USSR, considered MAD to be foolish bravado, and urged America to instead plan for proportionality, and thus even a limited nuclear war. With this logical reasoning, Kahn became one of the architects of the flexible response doctrine, which, while superficially resembling MAD, allowed for responding to a limited nuclear strike with a proportional, or calibrated, return of fire (see "Conflict escalation").