That will determine the U.S. role in the world more profoundly even than Sept. 11.
Sept. 11 spawned a U.S. war on global terrorism and major efforts to tighten homeland security. But it did not fundamentally alter the way the outside world works.
By contrast, defeating Iraq -- which U.S. forces could do, even if acting alone -- would thrust the United States into commitments abroad that must last years if not decades and, in the process, would transform global politics.
If he moves to war, President Bush will have the support of Congress and most, if not all, of the European allies. Russia and China will try to exact a price, but will go along.
And most of the unknowns in the "fog of war" could also break our way, to wit: Victory in Iraq might not lead to the overthrow of Gen. Pervez Musharraf in Pakistan, with its nuclear weapons, or of friendly governments in Jordan or Morocco. Israel might not be drawn into the conflict and inflame the Arab "street." And Israel might not suffer terrible casualties during Saddam Hussein's death throes, including from chemical or biological weapons, which surely he will try to use.
As the occupying power in Baghdad, the United States could not rely on fragmented dissidents to form a stable government, much less a rapidly developing democracy. This has not happened in primitive Afghanistan, where the economic requirements of fostering stability are so small. It is even less likely to happen in Iraq, with contending interests of outside powers, beginning with Turkey, and internal competitors for power -- not least the Kurds -- that are well-equipped to press their claims.
Throughout the region, rebuilding Iraq as well as Afghanistan would be viewed primarily as a U.S. responsibility -- at heavy cost, even if allies share the burden -- and a basic test of our staying power.
The United States also would face choices that will shape its role in the region for at least a generation. It could reapply itself to settling the Israeli-Palestinian conflict, embracing the view that it will become easier with Mr. Hussein out of the way. Or it could decide that a settlement is less urgent without Mr. Hussein to exploit Palestinian grievances and with others fearful of U.S. power. But the risk would be further delays in peace for the Israelis, and the Palestinians' remaining the "poster children" for those who rally support for Muslim terrorism against the United States.
Moreover, after victory, the United States must decide how to use its radically enhanced power and position in the Persian Gulf. Some argue that Washington would have less need to contain Iran and could support its president, Mohammad Khatami, in facing down the clerical relics of the Iranian revolution.
Others argue that the United States should either make Iran another Cuba or strike militarily, beginning with Iran's nuclear reactor, while U.S. combat forces remain nearby.
With Iraq as the world's second-largest oil repository, occupying it could break OPEC's ability to set global oil prices. But the United States would be expected to create a new energy structure that would provide widespread benefits, both an opportunity and a burden.
More broadly, the United States will need to decide whether Iraq is the exception or the rule. Will it have acted out of necessity against the growing threat of nuclear weapons in the hands of a psychopathic killer, or intended to become the arbiter of other nations' behavior, regularly backing its judgments with military power? Will the United States begin acting alone as a rule, or will it use its renewed record of resolve to re-energize alliances and promote international cooperation for democratic reform, peaceful change and the rule of law?
These choices will flow inevitably from a war in Iraq, perhaps even from dominating it through intrusive, disarming inspections. Whatever the United States chooses will require long-term engagement in the Middle East, which will impose major burdens on U.S. leadership, in the region and globally, and will entail high costs -- magnitudes more than current budgeting on foreign affairs.
This is the shape of America's future; we are already crossing its threshold.
Robert E. Hunter is a senior adviser at the RAND Corp. and served as U.S. ambassador to NATO from 1993 to 1998.