Hi Roger
I disagree about your suggestion.
There is a political angle you are overlooking here. The US is clearly trying to encircle and contain China. Mongolia wouldn't be the biggest piece in this chess game, but it could be a base for SOF. More importantly, having one more member sign on to an anti-Chinese alliance would embolden others. Other threads on SDF have mentioned that Chinese neighbors such as Vietnam are unlikely to sign on to such an alliance because they would bear the brunt of the conflict while the US would get all the benefits. If Mongolia is allowed to get away with this with impunity, it would embolden many other similarly situated countries too.
I hear what you are saying, but I still cannot get too excited about it. I tend to be with Walter and BD Popeye on this one.
I have heard nothing about this from the official Chinese Media and they are not noted for their reticence in displaying outrage when it is called for.
If it is a few instructors arriving on Civil flights, it will hardly constitute a major event. If it is about Mongolia's Peacekeeping in Iraq, there is no beef worth speaking off. If it is about combating Drug Trafficing through Mongolia to Russia, then all sides will support it.
Should the exercises however turn out to have a more mailign objective, then China and Russia can turn them into a farce, disrupting the arrival of US Military Carriers by open and closing the Air Corridors and seriously delaying their permisson to leave afterwards.
As you say, if Mongolia were to become openly hostile to its neighbours, it would be very easy to isolate.
So in summary, I think China and Russia have plenty of room to be; or at least appear, accomodating without losing face.