Russia is extremely unhappy about this expansion. They don’t have much of an army any more (it’s undertrained and underequipped by Western standards), so there is little they can do military-wise. They do have a few thousand nukes aimed at the United States and the EU but I don’t see those being used unless things deteriorate much further.
Former Soviet republics / satellites need friendly Russia as a trade partner much more than they need NATO or EU membership. Ukraine and Georgia do a lot of business with Russia. They are essentially shooting themselves in the foot out of nationalist/anti-Russian sentiment. Ukraine, for example, depends a lot on Russian oil and natural gas. If they do join NATO, Russia can, and probably will, refuse to sell them gas at any price. For a country at the latitude of Alberta with no oil or gas of their own, that would be fatal.
The defense shield is mostly a symbolic issue. Missile interceptors and radar stations in Eastern Europe can’t possibly be used as a protection against Russian nukes.
First of all, there are way too many of them. The system in its current state is lucky to intercept one or two ballistic missiles. It would have a snowflakes chance in hell of stopping a nuclear war.
More importantly, Russian ICBM trajectories don’t even pass over Eastern Europe. Washington DC-bound ICBM from Siberia would fly over Svalbard, Greenland, and Quebec.
