It is tempting for the United States to exploit its superiority in cyberwarfare to hobble the nuclear forces of North Korea or other opponents. As a new form of missile defense, cyberwarfare seems to offer the possibility of preventing nuclear strikes without the firing of a single nuclear warhead. But as with many things involving nuclear weaponry, escalation of this strategy has a downside: United States forces are also vulnerable to such attacks. Imagine the panic if we had suddenly learned during the Cold War that a bulwark of America’s nuclear deterrence could not even get off the...