The deaths of at least 20 U.N. workers and Iraqis–including Sergio Vieira de Mello, the U.N. Secretary General’s special representative in Iraq–were devastating in themselves. But like all acts of terrorism, the political target was just as important. That target was the reconstruction process itself, especially the prospect that Iraqi citizens or the international community could help the United States in its grand vision for Iraq’s democratic future.

In the past week alone, terrorists blew up the water supply to parts of Baghdad as well as the newly reopened oil pipeline to Turkey. The former was supposed to keep Iraqis alive in the searing heat of the summer; the latter was supposed to keep the new Iraqi government alive with some desperately needed revenue. Earlier this month, another car bomb killed at least 17 people at the Jordanian Embassy in Baghdad. Like the U.N. offices, the embassy was another so-called soft target, with less security than U.S. installations. And like the U.N. offices, the terrorists’ political message was the same: Stop helping the Americans in Iraq.

De Mello added crucial international credibility to both the civilian American administration in Baghdad and the new Iraqi governing council. British and American officials were pleased with his stature as the U.N.’s High Commissioner for Human Rights and his previous experience at the U.N.’s sister body dealing with refugees. But more than that, they were delighted with the Brazilian’s friendly manner and the smooth working relationship he established with L. Paul Bremer III, the top American civilian administrator.

For the Bush administration and the Blair government, de Mello filled the gap left by their reluctance to seek a U.N. mandate for the Iraqi occupation. Senior officials on both sides of the Atlantic believed the U.N. (represented by de Mello) would increasingly engage in the Iraqi reconstruction–either on the ground or by raising funds internationally–in spite of the lack of U.N. control in Iraq.

That process is unlikely to end with de Mello’s death. It might even be re-invigorated in a spirit of defiance against the terrorists who took his life. Yet the bigger barrier to international aid, especially in making Iraq more secure, is the lack of a U.N. mandate. India and France have already suggested they would reconsider their refusal to send peacekeeping forces to Iraq if there were another U.N. resolution to elevate the U.N.’s authority in Iraq.

Instead, the U.N. Security Council–even as it created de Mello’s job in Iraq–laid the entire responsibility for running Iraq on what it called “the occupying powers” of the U.S. and the U.K.. In line with international law, the U.N. stated in resolution 1483 that those occupying powers were obliged to restore “security and stability and the creation of conditions in which the Iraqi people can freely determine their own political future.”

De Mello’s presence in Baghdad never absolved the Americans and British from restoring security to Iraq. Yet his death underscores how they have failed to meet their obligations to stabilize the country–and how that failure is getting worse, not better, as the occupation continues. Of course it is unfair to blame American and British forces for the terrorist attacks and the sabotage in Iraq. Yet international law is strictly defined in this case, leaving no room to pass the buck: the occupiers are solely responsible for security.

That might sound legalistic, but it has a very real impact, especially after Tuesday’s bomb attack. It may be no coincidence that the attack on the U.N. followed last week’s resolution welcoming the new Iraqi governing council and creating the new, more permanent, U.N. assistance mission to Iraq. The terrorists are seeking to undermine both, and they have already spooked international governments and companies looking to get involved in Iraq. At one reconstruction conference with hundreds of smaller U.S. companies in Washington in June, the biggest concern–aside from getting a slice of the action from dominant contract-winners Halliburton and Bechtel–was how to protect any employees in Iraq.

They were not the only ones in Washington who have been alarmed by the lack of security in Iraq. On Capitol Hill, Republicans and Democrats alike have become increasingly public in their criticism of the U.S. occupation and the pace of the reconstruction. John McCain, the Arizona Republican who was one of the most hawkish legislators against Saddam Hussein, told NBC’s Today show that the U.S. needed more troops on the ground because of the “sophistication of these attacks”. McCain was speaking from Baghdad just hours before the attack on the U.N..

Other Republicans believe the administration is preparing for something very different. “The very people who pushed so hard for us to invade Iraq as soon as possible are the ones who are now saying we have to get out of Iraq as soon as possible,” said one senior congressional Republican. “I think we’ll be out within a year. It’s not our country and the Iraqis don’t want us there.”

Speaking in the Roosevelt Room in the White House last month, George W. Bush almost taunted the terrorists to strike in Iraq. “There are some who feel like the conditions are such that they can attack us there,” he said. “My answer is, bring them on. We’ve got the force necessary to deal with the security situation.” But in Crawford, Texas, on Tuesday the president showed little sign of those over-confident days in the early summer. Instead he hinted at how the White House was slowly but surely shifting the responsibility for security on to the Iraqis themselves. “The terrorists want to return to the days of torture chambers and mass graves,” he said. “The Iraqis who want peace and freedom must reject them and fight terror. And the United States and many in the world will be there to help them.”

Without sufficient U.S. troops to secure Iraq, and without the international help to back them, the Bush administration is edging towards blaming the Iraqis for their own misery. In spite of the defiant rhetoric–in New York and Washington–the attack on the U.N. in Baghdad may only hasten the day when the Iraqis find they have no security but their own.