When Iraqis in Baghdad celebrated America's arrival a year ago by beating a toppled statue of Saddam Hussein with their shoes - a sign of intense contempt - the White House was delighted. This was the kind of expression of glee at the departure of a dictator the US had anticipated.
Now one year later, the gruesome sight of Iraqis using their shoes to beat burned corpses - this time of Americans - has transcended the daily deaths in Iraq, and become a challenge to American will. At the very least, it raises questions about the depth of the US-led transformation there.
Wednesday's killings of nine Americans in two separate attacks - making March the second-deadliest month for Americans in Iraq - came at a point in the occupation that military authorities said would be dangerous. The United States plans to hand over authority to an as-yet undetermined interim Iraqi government on June 30.
But the events in Fallujah are part of a widespread uptick in violence against occupation forces and groups working with them, suggesting deteriorating rather than stabilizing conditions as the power transfer approaches. And while no one expects the upsurge to prompt a disengagement from a project that will define the Bush presidency in its reelection campaign, ongoing efforts to spread responsibility and reduce US exposure are expected to intensify.
The anti-American violence in Fallujah "won't have any large impact on the determination to stay the course in Iraq, there's no sudden groundswell of support for getting out," says Michael O'Hanlon, a military analyst at the Brookings Institution in Washington. "But it is one more data point as Americans assess how much they want to stick to this thing."
A building sense of chaos, fed by the anti-American violence, is the larger worry behind the initial horror of Wednesday's scenes, other observers say.
"The bigger issue here is the cumulative impact of the failure to stabilize the country and the continuing difficulty in arriving at an acceptable political transition," says Mac Destler, director of the program in international security and economic policy at the University of Maryland. "As you approach [the power transfer] you have a scenario of increasing attacks and political uncertainty that raises all the doubts and worries people had about this war. I'm sure they [in the White House] are scared to death of it."
Some analysts believe a political impact is possible. "This was the kind of thing that people could find just so shocking, horrible, it could jar them into reevaluating the prospects in Iraq, ... how things have been going," and whether the effort was worth it, says political analyst Stuart Rothenberg.
The scenes of American corpses being dragged by gleeful crowds through dusty foreign streets were reminiscent for many Americans of Somalia in 1993. Then, US soldiers in the African country as part of a peacekeeping force were killed in the shoot-down of a Black Hawk helicopter and then similarly mutilated and paraded through the streets of Mogadishu.
But there are many reasons this is not Somalia. Iraq is an American operation involving more than 100,000 troops that has occupied US political debate for two years. Somalia was all the more a shock because Americans had largely forgotten about US troops being there when they were suddenly confronted on the televisions with the shocking scenes.
"The US presence in Iraq is much more established in terms of awareness and support," says Mr. Destler. "Somalia came as a real shock, but Americans know about the dangers in Iraq."
With more than 500 US troops dead in Iraq, Americans are more accustomed to the violence. And military leaders had said to expect more violence, as antioccupation forces sought to take advantage of the uncertain political climate in the runup to the June 30 handover.
But the Fallujah violence also suggests that the broader picture that US military authorities in Iraq have been offering of the violence is not quite right. In recent weeks officials have backed up claims that Iraq is progressing - and settling into a new order with an eye toward building a stable democracy - by suggesting that most violence now was from non-Iraqi Islamic extremists. The domestic Baathist resistance nostalgic for Mr. Hussein, the argument went, was largely crushed.
Even after Wednesday's attacks, Army Brig. Gen Mark Kimmitt said at a Baghdad briefing, "Fallujah remains one of those cities in Iraq that just don't get it." But the geographical spread of recent attacks suggest something else, as does the exuberance of some average Iraqis in expressing anti-American feelings.
"There was evidence to back up those claims and it was plausible, but it wasn't proof," says Mr. O'Hanlon. "Now the suggestion from the ferocity and deadliness of these events is that if it's not Baathism or Islamic extremism that is driving these acts it might be something else, and that is a bigger worry."
Some experts suggest, for example, that a more typical Arab nationalism and visceral rejection of foreigners may be at the root of the instability - a sobering prospect at a time when the US is seeking not only to succeed in Iraq but to promote political and economic reforms throughout the Middle East.
Given the likelihood of more disturbing turmoil, the White House is both reiterating its "stay the course" stance and pressing ways to spread responsibility for Iraq and reduce American exposure.
The US is already relying heavily on the United Nations to broker a compromise on an interim government. And at the same time, the US is suggesting it will rely on a UN resolution to legitimize a continued US military presence in Iraq, rather than an accord with an interim government.
• Linda Feldmann in Washington contributed to this report.