Yeah, I doubt the US can really do much to Russia, I think if NATO getting involved in Ukraine and it's signed sealed and fully confirmed etc, then NATO HQ, Capital Hill, US congress, 10 Downing and other potentially threatening NATO leaders will be eliminated very quickly. Hypersonic Zircons will be used to take out key enemy leadership and throw the whole 27 country alliance into leadership crisis and then a ultimatum to back the fuck off. Russians know NATO (all together) too strong. However, I doubt a lot of NATO countries will get in directly, Belgium, France, Netherland, Germany, UK, US, Poland, Czech leadership etc. will get it for sure. The Turks, Greeks, Italians, Spanish, Sweds are pusses and Finnish will chill the fuck out, Portugese etc won't bother getting involved. Basically, going off known info, Zircon Mach 9, range at least 1000 km, shot from off the coast of Atlantic from sneaky subs or in North Sea can easily cover those countries who have taken a aggressive posture against Russia. However, such a strike has to be pre-planned, which it probably is, second needs quick decision making, I guess the Russians have prepared for this eventuality.
Also the moment, there's a confirmation of NATO/Russia collision on the news, the West will go into freefall, expect the worst crash in a century, expect massive run on banks for cash, people are not stupid. It will hurt the west way before a shot is really fired.