Now that the conflict in Georgia has returned to a simmer, it is time to reflect on some of the larger lessons. Perhaps the most important lesson is about the limits of America's ability to protect small, strategically exposed client states. Hawkish pundits and politicians insist that if Georgia had been a member of NATO, Russia would never have dared to use military force against it. Those confident assertions are wrong on two levels, and they underscore a dangerous flaw in U.S. foreign policy.

First, NATO membership for Georgia was not feasible at the time that Moscow launched its military operations. Even if Washington had been able to overcome the opposition of France, Germany, and other key allies at the Bucharest summit earlier this year, the most Georgia would have received was a Membership Action Plan. Tbilisi would still have had to meet a host of requirements before gaining admission to the alliance-a process that would have taken at least four or five years, probably longer.

Second, even if someone had waved a magic wand at Bucharest and made Georgia a full-fledged member, there is no guarantee that Russia would have been deterred. Hawks blithely assume that if NATO (in reality, the United States) gives an explicit security guarantee to an ally, no country will ever challenge that guarantee.  Since Article 5 of the North Atlantic Treaty proclaims that an attack on one member is an attack on all, so the logic goes, Moscow would never dare molest even a small NATO country.   That is a dangerously simplistic lesson drawn almost entirely from America's success in deterring the Soviet Union during the cold war.

Despite the cold-war experience, extended deterrence (protecting allies or client states) is hardly infallible. Indeed, history is littered with the wreckage of deterrence failures. Most Europeans in the early years of the 20th century assumed that the Continent's elaborate system of alliances would make war unthinkable. The tragic events of 1914 demonstrated how wrong they were. A generation later, the explicit British and French security guarantees to Poland did not deter Germany from invading that country.

The United States is certainly more powerful militarily than Russia, but the balance of military power is not the only consideration. Another crucial factor is the importance of the issues at stake to the protector compared to their importance to the challenging power-what might be termed the balance of fervor. That factor worked in America's favor in its confrontation with the Soviet Union. It does not do so today with respect to Russia.

America's principal Cold War security guarantee was to Western Europe.  The United States was prepared to put the safety-indeed the very existence-of its own country at risk. Policymakers considered that region crucial to America's own security and economic well-being, and they were determined to prevent the rival military superpower from gaining control.  It was reasonably credible to the Kremlin that the United States would be willing to incur significant risks-even the possibility of a nuclear war-to thwart a Soviet conquest.

Conversely, while Western Europe would have been a worthwhile strategic and economic prize for the Soviet Union, it was not essential to Moscow. Nor did Soviet leaders or the Soviet population have an emotional attachment to the region. There was, therefore, a definite limit to the risks the Kremlin was willing to take to gain dominion.

The situation today is radically different. It is far less credible to any Russian leader that the United States would risk war with a nuclear-armed Russia merely over a territorial spat involving Georgia-or even tiny countries such as the Baltic republics that are already members of NATO. The importance of those states to Washington is simply not comparable to Western Europe's importance to America during the Cold War. Conversely, Russia's quarrels with several countries on its borders involve an array of potent ethnic, economic, and strategic considerations.

To be blunt, the NATO commitment to small, vulnerable countries in Russia's immediate neighborhood looks like a bluff-and not a very credible one at that. U.S. policymakers have to hope that Putin or some future Russian leader doesn't decide to call that bluff.

If Moscow ever challenges Washington's commitment, the United States will be left with a choice between a bad outcome and a worse one. The bad outcome is that U.S. leaders face the reality that it would be reckless to risk a major war to protect a client that is of little strategic or economic relevance to America-even though a retreat would raise serious questions about the credibility of other U.S. commitments. The worse outcome would be to actually try to fulfill the security pledge and risk a war with nuclear implications.

The conflict in Georgia torpedoed the arrogant assumption that mere expressions of U.S. support for client states would deter other major powers. Washington suffered a blow to its pride and prestige, but the episode may have been a blessing in disguise. U.S. leaders need to understand that they have made a host of security promises that America probably cannot redeem. In essence, U.S. leaders have written security checks on a bank account with insufficient funds. They ought to rescind such unwise and unsustainable commitments before the next foreign policy train wreck.

Ted Galen Carpenter, vice president for defense and foreign policy studies at the Cato Institute, is the author of eight books on international affairs, including Smart Power: Toward a Prudent Foreign Policy for America (2008).  He is also a contributing editor to The National Interest.