Oh brother, he was explaining to tv audience how "The dead hand" aka "Perimeter" systems works.
If USA launches attack and manages to destroy even some of the command centers, the automatic sensors spread all over the country detect the strike and launch all-out counter strike automatically without need of involvement of command chain (destroyed at this point).
HE DIDN'T THREATEN TO NUKE USA But I guess sensational "news" headers sell better

Plus the guy in question is known for his somewhat odd remarks..