Both can happen; i.e., the Soviets or Chicoms or North Koreans
can indeed be planning to nuke us
and various terrorists also. Indeed, it would be a feasible gambit for, say, North Korea to plant a nuke and provide a false trail to some terrorist group.
Either or both.
I happen to believe that it is now inevitable that an American city will disappear; the only questions are 'when' and 'which city?'
Robert Heinlein, writing just after WW II, predicted that America would have to become a police state, with checkpoints at all major cities--every point of entry--to preclude smuggling in a bomb. IMHO it is amazing it has taken this long for his prediciton to come (almost) true. I believe the piece was If This Goes On....
--Boris
I think that is the reason the Nuclear Posture Review was "leaked" to the press. It was the administration's way of telling the world exactly what Fred said, and scaring the crap out of certain regimes, who might be having idiot fantasies about getting away with nuking an American city.