Although the fluttering in the West over the Russia-Ukraine gas dispute has ended for now, there is a deeper problem in relations between Russia and the West. Over the past several months, NATO has steadily crept into Russia’s backyard, romancing the former Soviet republics of Ukraine and Georgia with the prospect of membership in the alliance, and even hinting that NATO may attempt to intervene in the conflict between Armenia and Azerbaijan over the disputed territory of Nagorno-Karabakh. Unfortunately, it seems that poking the Russian bear is back in vogue.

On the heels of “color revolutions” in Georgia and Ukraine, those countries — both of which have prickly relations with Russia — have cozied up to NATO, much to the delight of NATO enthusiasts and Russophobes. NATO Secretary General Jaap de Hoop Scheffer told Ukrainian leaders in October that NATO’s door “was, is, and remains open” to Ukraine. Less than a week later, Secretary of Defense Donald Rumsfeld encouraged the Ukrainian government’s efforts to join the alliance: “Progress has been made [toward accession], and we encourage it.”

By November, Scheffer was using his same line to discuss potential Georgian membership: “Needless to say that NATO’s door is open.” Acknowledging the hot-button dispute between Russia and Georgia over the province of South Ossetia, Scheffer hedged: “NATO is following this, of course, with interest.” Even more brazen, NATO hinted that it would be open to deploying military forces to Nagorno-Karabakh.

NATO boosters ought to close the door of expansion, take a deep breath, and explain what, exactly, NATO’s mission is now. Equally important, they need to justify how it is in America’s self-interest for the alliance to acquire an ever-expanding roster of fragile and unpredictable client states on Russia’s border.

At the end of the Cold War, NATO’s purpose vanished. There was no longer a danger of Russian aggression against the West. Instead of disbanding, however, NATO took up an array of missions entirely unrelated to its original purpose — without bothering to define its new role. Relations between the alliance and Moscow are increasingly testy. NATO antagonized Russia in the late 1990s by circumventing the UN Security Council in attacking Russian ally Serbia. Now the alliance continues to poke at Russia by swallowing up former members of the Soviet bloc as fast as it can.

Advocates of continued NATO expansion express inexplicable surprise when Russia protests. By taking in the Baltic republics as members, NATO is already deeply involved in countries that have historically been well within Russia’s sphere of influence. The alliance seems poised to intrude further, and the Russian bear is beginning to growl. Nikolai Bordyuzha, spokesman for the Moscow-led Collective Security Treaty Organization, has made Russia’s views plain enough, warning that NATO bases surrounding Russia would constitute “a potential threat to Russia’s security.”

Russia — like any other country — tends to get alarmed when the world’s sole superpower extends security guarantees and military cooperation to countries on its borders. As NATO continues to expand, the United States has been hailing, and in some cases directly supporting, “color revolutions” that have caused instability and chaos in Ukraine, Georgia, and Kyrgyzstan. This is a dangerous mix from Moscow’s perspective.

It is also a dangerous mix from America’s standpoint. NATO is much more than a political club. It is a military alliance with serious obligations for the United States. Article 5 of the North Atlantic Treaty proclaims that an attack on one member is an attack on all. That means the United States is obligated to defend every member no matter how small, how militarily and economically insignificant, or how strategically exposed that member may be.

And those obligations go on forever. Therein lies the danger. True, there is little risk of a clash with Russia in the near term. Russia’s military is in no condition to challenge the United States, even in Moscow’s backyard. Moreover, Vladimir Putin has adopted a surprisingly accommodating policy in an effort to secure economic and political benefits from the United States and its allies.

But who knows what Putin’s successor might be like? Who would dare predict the political environment in Russia a decade or a generation from now? All that would be required to trigger a crisis is a Russian president who tires of a neighboring state’s treatment of its Russian inhabitants as second-class citizens and decides that Moscow should rectify that situation by force if necessary. Indeed, a crisis could be triggered if a future Russian president concludes that a Western military presence itself is an intolerable intrusion into what should rightfully be Moscow’s sphere of influence. And a Russian president might well conclude that the United States would not really risk war over South Ossetia or a similar obscure conflict.

We don’t need to treat Russia with kid gloves, but reasonable caution and consideration is in order. Russia has a sound right to wonder about NATO’s motives: Whom, exactly, would Georgia, Ukraine, and other potential member-states be allying militarily with NATO against?

The West can continue to press forward with NATO expansion indefinitely, antagonizing Russia and entering into security guarantees with countries on its border. But that course is unreasonable if we expect Russia’s cooperation on nuclear proliferation, terrorism, or other issues vitally important to America. If the United States values those goals, let alone long-term peace with Russia, it needs to engage Moscow, not unnecessarily antagonize it.