I cannot pretend to understand the calculations that Stoyan Sarg has conducted to come to the conclusion that two coincident nuclear ground based atmospheric detonations would cause, but I can say that the self sustaining vortexes he describes stripping the planet of first the atmosphere and consequently the water are the biggest existential threat which should be taken seriously if it hasn't already.
A single bomb dropped on the US would, of course, not end the US, in fact the response, as you identify would likely be far more devastating for more souls and disruptive to the way the world currently functions.
What I suggest is that we should be prepared to use whatever ways and means we have in order to prevent that first bomb from reaching its target.
I think you worry too much. It isn't an ICBM but an IRBM with a range of a few hundred miles. It could reach Japan's southern coast...
OTR radar was tried at Orfordness in the UK during the 60's and 70's, it was a VLF radar called Cobra Mist. It was so powerful that shipping was banned for12 miles out to sea, the VLF radiation would have killed any sailors who got too close. It a National Trust property now.