The system set to be installed in Poland were mid-course interceptors. They would not have been effective in defending the US from Russian ICBMs due to the ballistic path mismatch. If they wanted to protect Europe from Russian short and medium range missiles, THAAD would be a better option. The missile defense destroyers recently deployed to the Med are there to send a message to Iran, as are the radar stations in Turkey.
Russia has been historically against any effort by the US to develop and implement a missile defense system. Why? Simple: Since 1973, their military hardware and doctrine have been defeated. In a head to head matchup against the Weat in a conventional war, they'd lose badly, even in the deteriorating conditions in which the US military currently finds itself.
The only true threat they pose is their large nuclear arsenal. Negating that with a defense system diminishes them considerably.
The former head of President Reagan’s anti-missile defense Pentagon program, Colonel Robert Bowman said in 2009, that the developing of a US Anti-Missile Defense “shield” around Russia, far from being defensive, is offensive in the extreme.
A Russian Topol-12M mobile nuclear missile. In the worst case scenario, a nuclear missile could be fired in to space that would release a pulse large enough to paralyse, for instance, Great Britain’s infrastructure, defence experts warn .
Russia could also deploy Iskander missiles, which are believed to have a range of more than 300 miles, in the Kaliningrad exclave that borders EU members Poland and Lithuania. The same missiles could also be deployed in southern Russia close to Georgia and Turkey.
It is better not to poke the bear in the ribs.