They claim we can't do anything about it. They also used to claim that they had all these fancy-schmancy missiles ready to destroy America, but when Gorbachev allowed inspectors in, many of those missiles turned out to be duds, fakes, or inoperable because Russia's economy had been so bad for so long they couldn't maintain them.
I have no doubt Putin has a few missiles that would pose some problems for America. I also have no doubt we are fully aware of those missiles and their capabilities thanks to our spies, and we've got a defense planned, if not fully implemented, already. There's very little they're doing that we don't know about, and vice versa.
The question is, why on a random Thursday would Putin announce something like this, something almost akin to a declaration of war, when he's been going on and on about how America & Russia should be friends for the past year? What's he hoping to accomplish by pulling back the hand held out in friendship and replacing it with a pistol pointed at our head?