From what I've read on the matter (and it's way more that few journo articles) it is hard to say whether the American 'promise' was given for E. Germany or for E. Europe as a whole, and either way it was never put through relevant paperwork and transformed into solid deal. Even if it was blatant lie, which it probably wasn't since Baker at the time had no vision on NATO's expansion, an even if Genscher was more direct on the same matter, Russians came of more as a sore losers than anything else.

In the end one could easily point the finger at Gorbachev and Shevardnadze for not doing their jobs on that matter. Very poor statecraft performance from that lot.