Robert Heinlein pointed out that there is no such thing as a nuclear bomb shelter, only a fallout shelter (for all practical purposes, obvious exceptions such as Cheyenne mountain)
The expected life of Cheyenne Mountain during an attack from the Soviets was less than an hour. At this time the Norks can't get a nuke there but even when they get a long-range delivery system it will be a long time for them to attain the accuracy necessary to hold hard targets at risk, unless another country gives them better guidance systems.