Nobody has ever explained how NATO expansion actually "threatened" Russia. What, were the Germans suddenly going to reconstitute the First SS Panzer Army and drive for Moscow? It's completely ludicrous. Everyone, including the Russians, knew that most of Europe has zero appetite for wars of aggression. Literally
none. Europe didn't even have enough of an appetite to spend 2% of GDP for its own defense.
And on top of that, nobody is stupid enough to invade the homeland of a nuclear-armed country. That alone protects Russia from invasion by NATO.
The only thing NATO "threatened" was Russia's desire to threaten/intimidate/bully/conquer her neighbors. That's it