Furthermore you assume that Russia wont immediately call in all their chips to get it done. They have been chomping at the bit to get this missile shield down, including using our own START treaty renewal to argue that it made the missile shield illegal.
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Of which they knew NATO would not agree to a joint system as Russia's military dealings with Iran would make such system void of any purpose.
Which is a failed argument, if they wished to use it as a noise they would not have gone the radical step of actually attempting to use the START treaty to stop the missile shield, and even saying that by continuing it, it would make the START treaty void.
You seem to have this rather false belief that Russia is looking for the status quo, despite the fact that not only have they become a vocal supporter of Iran at the UN, but also have attempted to shut down the missile shield at every turn. Not to mention the fact that Russia has a sizable military and economic intrest in Iran due to it's trade in war assets and economic assets with the country.