NATO could definitively deter Putin from ordering the use of tactical battlefield nuclear weapons by making it crystal-clear that any such use will result in instant obliteration of Russia. What will actually happen, however, is that in the event Putin does order such use - and Russian forces obey (which is not a given) - NATO will release a flurry of empty words, do nothing meaningful, and then issue various "reasons" why doing nothing is always the best option when faced with extreme aggression.