Sad to say, I'm not even certain a "Perfect Day" attack would bring the appropriate response.
Yes that question remains to be answered. I suspect a real nuclear detonation would produce such a virulent public reaction that some sort of really strong retaliation would be launched. Other kinds of things using radioactive material or mass poisonings or some combination would produce a more muffled reaction. Interestingly some of the really violent islamaits really want to trigger a massive US retaliatory response. They believe that they will be able to crawl out of the ruins and grab control of many Muslim countries and begin to rebuild the Caliphate. If it takes a thousand years it doesn’t matter. It is the ‘Will of God’ and that will mist be obeyed. The deaths in a really horrible way of tens of millions of their coreligionists is of no interest to these people as their deaths are just a means to the ‘Noble end’ and are therefor either expedient or , considering how lapsed many Muslims seem to these people, a deserved punishment. This is like dealing with Nazis who see the road to the ‘Triumph of the will’ to be through mass destruction. This is another very disturbing aspect of the war we are in (that we cannot call a war).