What are we doing on Russia's doorstep? Why giving the very nations, the Soviet Union (Russia) historically occupied before, during and after WWII a sense of security.
Remember, Russia armed, directed and lead rebels in Eastern Ukraine and occupied The Crimea (part(s) of a sovereign nation) and Russia in support of those rebels sent in some units of their military and the very same country fired upon the military of that nation.
Now why would "Estonia, Latvia, Lithuania, Romania, Bulgaria and Hungary" be worried about their ex-Warsaw Pact partner. As a side note almost every Ex-Warsaw Pact member is now a member of NATO. Now why would they want to do that when their friendly neighbor Valdimir is so willing to help them...
Life is like a PB&J sandwich
The older you get, the moldery and crustier you get.
Now, get off my grass!