I have read elsewhere that Serbia and Russia are in discussions about establishing a Russian base in Serbia. Maybe other FReepers can comment on the specifics. I don’t know if anything will come of this, but Serbia needs Russian support to stand up to the EU and NATO. I suspect that any reaction will be economic and not military. The US has succeeded in creating a terrorist mini-state in Europe - the world turned upside down.
How would Russia get access to Serbia? The country has been land locked since Montenegro, which provided its only access to the Adriatic Sea, became independent in 2006.
If reaction will not be military, what use would the Russians have for a MILITARY base?