There were elaborate explanations Thursday as to why the Russian president, Dmitry Medvedev, had chosen to greet the election of a liberal to the White House by deploying nuclear missiles in its western enclave of Kaliningrad.

Russia, we were told, was laying down a marker. It was saying: you cannot ignore us. Or Medvedev was testing a greenhorn leader to see how he would react. There was every explanation except the obvious one: cause and effect.

The cause was America's decision to deploy missiles and a radar system on Russia's border. It was a decision which no Russian president of any hue could ignore. The radar is capable not only of tracking incoming Iranian missiles but of directing a warhead anywhere on Russia's territory to an accuracy of metres. Try as Russia might to talk to America, Washington would not be deflected from its course. Sergei Ivanov, then first deputy prime minister, warned in July 2007 that if America did not modify its plan, Russia would station missiles in Kaliningrad. Now it is doing so. That is the effect, so where is the surprise?

One move in this poker game soon leads to another. Thanks to America's insistence on a shield of unproven worth, and Poland's backing for it, eastern Europe now faces the nightmare return of the short-range missile. Go back 16 years to discover just how dangerous this bluff was. Taking the chips off the table is going to be more difficult, even though Barack Obama told Radek Sikorski, the Polish foreign minister, about his doubts concerning the effectiveness of the missile shield. Whatever the truth about the Pentagon's claim that the shield is not aimed at Russia, the installation has become a self-fulfilling prophecy.

It invites Russian targeting, from which the missile base now has to be defended. The result is that missiles are springing up like green shoots. And no one can afford to wait for the next frozen conflict of the region - an area that runs from the Baltics, through which Russian military convoys travel to Kaliningrad, to the Caspian Sea - to leap out of the deep freeze. Georgia could erupt again.

The Kremlin is not blameless: it is nationalist, autocratic, the battleground of rival clans capable of provoking a conflict in the Caucasus for the purpose of sending a message to each other. But the regional stakes are now getting high. Mr Obama has to convene an early bilateral summit with Mr Medvedev and Vladimir Putin, his prime minister. The two sides need to untangle the issues dividing them, not tie them ever tighter into an intractable knot. If he does nothing and gets dragged in by proxies such as Georgia, Barack Obama's first international emergency may not be Iraq or Afghanistan but Russia.