Russian Missiles to Kalaningrad

The Russians legitimately see the BMD system in Poland as a threat, and they are taking what they see as appropriate action. (See also here)

This was foreseeable. It's natural for the Russians to see the system as a direct challenge, particularly since the location of the interceptors and radar are better more suited to protecting Europe from Russia than from Iran, which is the putative reason for the installation in the first place.

It's also a challenge to Obama, which complicates things, because it makes it harder for him to do the smart thing, which is to relocate the installation further south or cancel it completely.