The Hurricane Katrina disaster is one of the greatest ever to hit the United States in its physical and human scale, while politically it is certainly on a par with the 9/11 attacks, the fourth anniversary of which falls tomorrow. The two catastrophes will frame George Bush's presidency.
While the major relief and rescue effort is now well under way, the inept delay in starting it after the hurricane struck and the New Orleans levees broke, leaving so many people trapped and killed, will be controversial for years to come. Mr Bush is seeking to marginalise that impression by mounting a huge programme of rehabilitation and reconstruction costing over $60 billion so far.
But this is a political as well as a humanitarian watershed for his administration. Never in the history of any disaster in the First World, was it reported that people were abandoned and left to die. The hurricane probably marks an end to the era of smaller federal government in place for the past 20 years and is bound to affect Mr Bush's other main priorities. It reveals a new vulnerability of the world's sole superpower, as symbolised this week by the humanitarian aid promised to its people and government, to which Nato added yesterday with a commitment of ships and food.
These are strong gestures of solidarity, and appropriate ones, given the scale of the disaster. But it would be a mistake to underestimate the psychological jolt involved for the American people. This is symbolised by the reluctance to talk of American refugees in their own country, after the disaster struck a region three times the size of Ireland, and with those affected distributed now in an area the size of western Europe.
Social and racial divisions have been cruelly exposed by the disaster in another blow to conventional American self-understanding. As Colin Powell said yesterday in his criticism of the way the disaster has been handled, poverty underlies the profile of suffering, in which black people were so overwhelmingly left in the city after the more affluent white population departed before the hurricane struck.
Americans now face a huge challenge in repairing the image and the reality of these divisions. A great deal will depend on how New Orleans is rebuilt and whether its social divisions are tackled or reproduced as this is done.
The economic and environmental effects of the disaster deepen by the day. World energy prices and supplies have already been hit, as reflected in yesterday's announcement of gas and electricity price rises here. While the massive federal rebuilding programme will stimulate the US economy next year, consumer confidence may lose its buoyancy, creating ripple effects elsewhere. The environmental damage to the Gulf coast and its famous wildlife and seafood is immense. The next generation must draw on the lessons for conservation and climate change.