https://www.bloomberg.com/politics/graphics/2016-nuclear-weapon-launch/?
"The senior officer in the Pentagon war room must formally authenticate that the person ordering the strike is indeed the president. The officer reads a “challenge code,” often two phonetic letters from the military alphabet, such as “Delta-Echo.” The president retrieves the “biscuit,” a laminated card the president or military aide carries at all times, and finds the matching response to the challenge code: “Charlie-Zulu,” for instance."
Assuming it was a nuke, some or more of the various codes were comped/sold/leaked (hmmm - America for Sale?). Maybe it wasn't someone in the US CoC that "authorised" the launch, hence unauthorised?