Including each other? That's the essential bit. Do either side have the capability to respond after a devastating, no warning first strike? That's what the arms

Including each other? That's the essential bit. Do either side have the capability to respond after a devastating, no warning first strike? That's what the arms race was about. Both sides have such extensive overkill capacity because they are expecting to face off against each other and need to be prepared for only a small fraction of their armament surviving a first strike or capable missile defenses.