I follow and agree with your logic ie nuking a Russian city in retaliation would pretty much result in madd.What would be the proper response?How long for China to fit those cruise missles w/nukes?I read some time ago that China may have stolen 20 to 30 yrs of /nuclear weapons tech from Los Alamos(?)in the 90's.Was the article correct?
One thing i do know is that their naval capabilities have been brought forward by almost 3 decades in the span of one. That is obviously not due to Los Alamos by any measure, but it is still a significant jump.
As for the need for a proper response. I personally think that the best thing to do would be to ensure that no response is necessary. By doing our best to not leave loose ends about that can come and bite us. However if worst came to worst all we could do is strike at the offender (if we can come up with a definite target since most likely that attackers will be an amorphous target like Al Queda).
The best thing is to ensure this doesn't happen in the first place. If an American city is nuked it really will not matter much what we do from there, because the result will either be bad or worse!