You are coming at this from an odd angle, but the main approach is that in the USA the way this has been looked at has been to try and make sure that only the civilian executive (the President) has control over whether or not nuclear war can start or not. In later years the Secretary of Defense's consultation/consent has also been required but it is not clear how binding this is (e.g., can the President override, or just fire, the SecDef?). But the main issue has not been about preventing the President from starting a nuclear war, but making sure that only the President can start a nuclear war (and not a random general or lower-level military figure).

In practice this has proven to be quite a tricky logistical and strategic issue, because there are instances in which it has been desirable to "delegate" that command authority downwards, say, to people on the front lines in Europe who might need to use tactical nuclear weapons to avoid being overrun.

A brief sketch of these policies: In the 1940s, the bombs themselves were split into their nuclear and non-nuclear components, with the nuclear components kept in the custody of the civilian Atomic Energy Commission, who answered only to the President. So the AEC would literally have fought the military if the military tried to take the bomb cores. Later choices in bomb technology meant that this separation became impossible, and after the USSR got nukes the need to respond rapidly also made this logically cumbersome. So under the Eisenhower administration some 90% of the US nuclear stockpile transferred to the military, and many divisions were "pre-delegated" to use nuclear weapons under certain conditions, without orders from Washington. The Cuban Missile Crisis scared Kennedy enough to think this was immensely dangerous, because it could lead to a small-scale mistake escalating into all-out war, so he required all foreign-based nuclear weapons to have specialized locks on them to prevent their use without Presidential approval (PALs), and eventually the domestic forces as well. Increasingly sophisticated Command, Control, and Communications systems were developed to create electrical means of preserving command authority with the President. The degree of delegation/pre-delegation is not currently known — it has probably not completely gone away.

But the system is not set up to prevent the President from starting a nuclear war. It is set up to prevent anyone else from doing it.