This is such a lame desperate ahistorical talking point. Written "assurances" between states are called treaties. There was/is no treaty between the USSR, Russia, USA or NATO that states NATO would or will not accept new members. The principal actors were all very intelligent professionals, if they wanted a promise there would have been a treaty, there wasn't one. As much as the American and Russian officials want to think they are the center of the world they can't decide things in private on their own. Russia might have wanted that but they were not in a position to demand it so it didn't happen. We are talking about mature societies of 100 million people who had just been brutalized by the Russians 50 years, should we really have thrown them back to the wolves because a few Russians might get upset?