Russia will not allow any sort of US missile base (defensive or otherwise) in her sphere of influence.
I just hope we are not so crazy as to put one there.
Since Russia has decided to provide Iran, a criminal regime, with nuclear technology, Russia has exited the community of civilized nations, and has no right or claim to anything, or any respect or deference from, any civilized country.
They can reverse their barbarism tomorrow - but at present, they are an illegitimate troublemaker and there is no reason we should pay the slightest attention to anything they say. And spare me talk of their threats or on the other hand of their assurances - deliberate proliferation of nuclear technology to terrorist criminals, destroys any basis for discussion of any kind.
Clear enough for you?
Russia has choice in the matter I am sure. The motherland can give up arming Iran and Syria with nuclear weapon design and materials and we can stop arming our allies with defensive counter-measures. Until then I see this arms race accelerating.