Throughout US history - from the 1898 Spanish-American War to Vietnam - nearly every major conflict has produced some domestic political backlash as the public debates the legitimacy and cost of military action.
It's a pattern of democratic dissent that has curbed use of US military power, historians say. And Iraq is no exception. As the death toll among US forces steadily rises and bills for the occupation roll in, support is eroding not only for the scope of involvement, but for the overall US strategy of preemptive war, experts say.
In essence, Americans seem to be asking: "Can we afford the Bush Doctrine?"
"The election in 2004 is going to be a referendum on the empire," says Andrew Bacevich, a professor of international relations at Boston University. Success or failure in Iraq will determine if "the imperial project can remain on course," he predicts, referring to what critics view as the administration's agenda of toppling "rogue" regimes.
Most Americans - from all political parties - say that, following the Iraq war, they oppose a policy of using military force against another country unless the US is attacked first. Polls also show that Americans do not support waging war against Iran or North Korea, even if those so-called "axis of evil" countries are developing weapons of mass destruction.
Such attitudes contrast sharply with the administration's national security strategy, also known as the "Bush doctrine," which lays out the president's intention to use preemptive military force against perceived imminent threats. "We cannot let our enemies strike first," it says.
To be sure, just as Sept. 11 rallied the public behind higher military spending and more aggressive missions, another major terrorist attack could do the same. Already, since the 1989 fall of the Berlin Wall, the US has deposed five regimes - roughly one every three years, notes Andrew Krepinevich, director of the Center for Strategic and Budgetary Assessments. "We are in the business of regime change," he says.
Today, however, most Americans believe the preemptive use of force in Iraq has left the US at greater risk for terrorist attacks. Moreover, a public that was united behind the war in Afghanistan is increasingly polarized over the conflict in Iraq. Pro- and antiwar views on Iraq are following traditional lines of party and gender, with the strongest opposition voiced by Democrats and women.
"Iraq now looks a lot more like the [military] missions of the 1980s, with Democrats a lot more leery of preemptive war than they used to be," says Carroll Doherty, editor at the Pew Research Center for the People and the Press. "The public is split on whether it really wants the US to be the policeman of the world. The bottom line is not global empire, it's protection."
Overall, support for the war in Iraq, while still strong, is slipping. Americans worry that the war is going badly, that the 130,000 US troops in Iraq are overextended, and that no clear exit strategy exists, even as soldiers are killed almost daily.
Above all, substantial majorities of taxpayers are balking at the administration's $87 billion supplemental request for Iraq and Afghan-istan, exacerbated by lower-than-expected contributions from allies and meager Iraqi oil revenues, polls show.
"The public was totally unprepared for the $87 billion request. They had no idea they were getting into a grand project to remake Iraq or the entire Middle East," says David Hendrickson, an expert on the history of American foreign policy at Colorado College.
The reaction to Iraq crystallizes an old contradiction in US policy, "to want to rule the world without paying the price," he says. "The gap between the aspiration and the willingness to bear the burden is ever wider and more unsustainable."
Apart from the financial burden, stress on US troops is another check on the Bush doctrine. It is raising concern among the uniformed military and especially in the Army, which bears the brunt of the crunch. Army leaders have called repeatedly in recent weeks for increasing the ranks of infantrymen, military police, and civil-affairs troops - all in high demand in Iraq.
"We don't have the military resources to do much else ... we're not going to do another Iraq," says Allan Millett, a military historian at Ohio State University.
Heavier-than-anticipated reliance on the National Guard and Reserves - with 170,000 mobilized and war-zone duties stretching beyond a year - underscores the manpower constraint.
"We're going to run out of [troops] before we run out of money, because it's an all- volunteer military," says Mr. Krepinevich. If the war continues to deplete resources, it will discourage regime change, he says - barring a major terrorist attack.
"The key," says David Tretler, a strategist at the National War College, "is the degree to which Americans feel threatened."