If the escalation is called for, the Russian Poseidon (status-6) nuclear torpedo can take out a carrier strike group. People think they are designed for coastal cities, but I think they are for carrier strike groups and possibly for naval bases. The US has projected power from aircraft carriers for a long time with no good counter, so my guess is that this is the counter. Blowing up a nuke in the ocean isn't going to be seen as horrible as blowing up cities with a nuke, since only military assets will be destroyed and the radiation fallout will be remote and the US blew up south pacific islands over and over and over again so it's safety profile is fairly well known.