Leading article: Katrina has exposed ugly truths about America

It was on his watch that federal funding for reinforced flood defences was cut and warnings about the scale of the all-too-likely catastrophe ignored. He was head of the executive branch of government that responded so slowly to the evidence that a rich American city was sliding into chaos. And he was Commander-in-Chief of the world's most powerful military as it found itself impotent.

It is not only his fault, of course. The whole city of New Orleans could be regarded as an unwise venture, built below sea level on foundations of greed. The draining of the protective wetlands had been going on long before Bush became president in 2001. Nor was there any reason for city and state governments not to have taken more responsibility for contingency planning. But even hard-line Republicans hostile to big government regard emergency relief as a federal responsibility and have found President Bush wanting.

Even hard-line Republicans who distrust state intervention to alleviate poverty will have been horrified by the extent of social division revealed by the flood. George Bush made a crass joke about Trent Lott, the former Senate Republican leader, losing his house in Mississippi, which implied that nature had not discriminated between rich and poor. As the President laughed, the dispossessed urban poor, overwhelmingly black, were still dying or pleading uselessly for food and water for their children.

One of the starkest choices between Bush and Kerry in last year's presidential election was in the redistributive effects of their tax plans, and the American electorate chose to avert its eyes from the desperate poverty of the mainly black underclass concentrated in the parts of cities to which white car drivers rarely go. Four decades on from the civil rights movement, race remains the starkest dividing line in American society. As Rupert Cornwell writes opposite, the way poverty in New Orleans has floated like jetsam to the surface of the national consciousness could have profound consequences for American politics.

The hurricane could have other effects on American attitudes. Even oil-rich Republicans could not fail to notice some of the connections between lifestyles and environmental sustainability that have been exposed by the disaster. Global warming may have made the devastation worse. Hotter seas seem to be increasing the intensity of hurricanes, though the jury is out on whether it is making them more frequent. But the connections range much more widely than that. The US should now understand better its need to respect natural forces and its dependence on oil.

As shock events sometimes do, Hurricane Katrina has exposed some half-hidden truths about Bush's America. The urban poor were trapped by floods in conditions resembling fictional nightmares from Lord of the Flies to Blade Runner as the affluent drove away. The disaster has dramatised some of the consequences of America's profligate attitudes to natural resources - with the news bulletins of the past week resembling an extended parable on the costs of environmental despoliation. But most of all, the storm has exposed the shortcomings of a weak President and his misguided policies.