Think again. Yes, the dollar is dropping faster than America’s prestige. Once more, the United States is going through a period of self-doubt and self-inflicted weakness, and lesser nations like Iran keep rubbing it in by reaching for nuclear weapons while hammering away at Washington’s position in the Middle East. But who would take care of business if the United States were truly down and out?

Moscow? Vladimir Putin’s neotsarist Russia is a revisionist power seeking revenge for a dozen years of humiliation—real or imagined—at the hands of the West. Revisionist powers want more for themselves, not responsibility for the rest. Why would the world want to entrust order and stability to a country that is on an expansionist roll and does not even understand its own best interests? Russia should do its utmost, for example, to stop Iran’s headlong dash for nuclear weapons. Yet Moscow has turned into an undeclared protector of Tehran instead, sabotaging painstaking international sanctions and warning you-know-who against military intervention. Russia is also manipulating local conflicts to reassert its power over the “Near Abroad”—those countries that once were Soviet republics. Bullies should not become class presidents, and the idea of a resurgent Russia’s shouldering the burden of world order is not an enticing one.

What about China? Unlike Russia, China is integrating itself into the world economy, which requires respect for the rules. Beijing is also quite cautious when it comes to converting its breathtaking economic growth into military power and ambition. But a pillar of a liberal world order it is not. Like Russia, China seeks more for itself rather than for the whole. It puts energy and raw materials über alles. Thus Beijing shelters the government of oil-rich Sudan, even though Khartoum is engaged in deadly ethnic cleansing in Darfur. China also dragged its heels when it came to pressuring North Korea on its nuclear weapons. And like Russia, China is protecting Iran’s Mahmoud Ahmadinejad against sanctions that would really bite.

Europe presents the opposite problem. The EU does demonstrate a sense of order beyond borders. It supports democratic development, peaceful conflict resolution, open trade and a rigorous climate policy. But for all its fabulous riches—with an economy as large as the American one—it does not generate power commensurate with its assets. How could it, when the largest EU member, Germany, spends the same proportion on defense as the smallest, Luxembourg (1.4 percent of GDP)? The U.S. share is three times larger. Germany fielded 7 million soldiers during World War II. Today, it can barely handle sending 8,000 abroad. Still, Europe’s real problem is not resources, but will: it does not have a global vision or a grand strategy. And no wonder. The EU is not a state, but a collection of 27 nations that must hash out a common interest by way of tedious compromise. In economics, that works beautifully; in the strategic realm, it does not.

So who would mind the global store if the United States did not? Washington is still the only world player with global interests and the means to match. It was the United States that finally acted to stop war in the Balkans. It was the United States that orchestrated the multilateral diplomacy that persuaded North Korea to stop its nuclear-weapons program. And if anybody can reanimate the peace process between Israel and the Palestinians, it will not be Brussels, Beijing or Moscow. Only the United States has the will and the wherewithal to guarantee the security of both sides. Similarly, if the United States bolts from Iraq, no one will be left to prevent partition and mass mayhem.

The problem is that the United States hasn’t exactly acted as a pillar of stability in the recent past. Succumbing to imperial temptation, it has spurned friends and international institutions. Theoretically, the solution is quite simple: this über-power must close the gap between its enormous strength and its damaged legitimacy. Coercion does not win friends, and vast power, especially when liberally used, generates counterpower, resentment and resistance. So strength must be tempered by responsibility.

The next occupant of the White House might well remember the golden age of American diplomacy in the second half of the 20th century, when Washington pursued its interests in a host of international institutions—from the United Nations to NATO, from the IMF to the WTO—which were built and maintained by the United States. They all had one common denominator: they served U.S. interests by serving those of others. It was not goodness but prudence that turned overwhelming might into leadership.

Or, to put it in coldly strategic terms: if Mr. Big does not contain himself, others will, and the “city upon a hill” that the pilgrims sought to build in the New World will become a high but very lonely place.

Joffe is publisher-editor of Die Zeit, a fellow of Stanford’s Institute of International Studies and Hoover Institution, and the author of"Überpower: The Imperial Temptation of America."