I am, however, in agreement with Robert Kagan when he argues that American predominance will persist long after the Iraq War:
... foreign policy failures do not necessarily undermine predominance. Some have suggested that failure in Iraq would mean the end of predominance and unipolarity. But a superpower can lose a war — in Vietnam or in Iraq — without ceasing to be a superpower if the fundamental international conditions continue to support its predominance. So long as the United States remains at the center of the international economy and the predominant military power, so long as the American public continues to support American predominance as it has consistently for six decades, and so long as potential challengers inspire more fear than sympathy among their neighbors, the structure of the international system should remain as the Chinese describe it: one superpower and many great powers.
One note of caution, though: Kagan persistently refers to our main potential challengers, China and Russia, as "autocratic" nations, which strikes me as a confusion of terms. And this confusion makes him less attuned than perhaps he should be to the possibility that the current Chinese model of government, in particular, might increasingly inspire sympathy (and emulation) as well as fear. I'm no China expert, obviously, but it seems to me that the People's Republic has moved steadily away from the autocratic model of Mao and Deng, and toward what might be described as a one-party meritocracy - a rule by the best and the brightest in which the path to power for a talented individual is open enough to co-opt precisely the kind of people who would ordinarily be leading agitators for democracy. Whether this model is sustainable in the long run remains to be seen, but if you're a developing nation looking for a path to modernization (or, perhaps, a particularly anti-populist EU bureaucrat), the Chinese system promises all the benefits of liberal democratic capitalism without the messiness of, well, democracy. I'm still enough of a Fukuyaman, even now, to suspect that China will eventually democratize, but in an unstable world with an interconnected global elite, I think we underestimate the ideological appeal of an undemocratic meritocracy at our peril.