Hurricane Katrina has posed some fundamental ideological questions. Most obvious is the proper balance between state and federal government. Americans are asking why federal help did not arrive earlier. After the 1906 earthquake in San Francisco, federal aid arrived within two days. A century later, New Orleans had to wait five days before an all-out relief operation was launched. The more information emerges, the more irresponsible the federal authorities appear. The Bush administration cut funding from New Orleans levee maintenance projects. And the Federal Emergency Management Agency was undermined by the creation of President Bush's new Department for Homeland Security. After Katrina, Americans appear to want a leadership that can make federal government work again. But can the Republican Party with its narrow emphasis on "small government" fulfil that role?

The other question posed by Katrina concerns the social fabric of America. The vast majority of those who have suffered and died in New Orleans were poor and black. We now know that a third of the predominantly black population of New Orleans lived below the poverty line. According to some prominent black politicians, this is the reason the relief operation was so slow. This does not appear to be a minority view. Indeed, the disaster in New Orleans appears to have provoked wider concern at the social condition of black people throughout America. There are ghettos not unlike New Orleans in many American cities. After witnessing the appalling scenes of last week, an unusual number of voices in America are beginning to demand change.

For decades, the American right has preached the superiority of self-help and discipline to social spending. And the Bush administration has gone about implementing this philosophy. Had Katrina not come along to shatter the routine of Washington politics, the agenda for Congress this week would have been cutting the Medicare programme. But are Americans beginning to seek different solutions?

President Bush is now under pressure as never before. His opinion poll ratings are low. And it is widely believed that he responded badly to this latest crisis. Pressure on the President to make a conciliatory gesture to the mainstream by appointing centrists - rather than right-wingers - to the Supreme Court will grow. Yet there will also be pressure from within the Republican Party for the conservative revolution to continue. With Supreme Court judges appointed for life, here is a political choice that could influence US society for a generation.

American politics is at a crossroads. Many preconceptions are being battered by natural catastrophes and the consequences of human folly. The question now is whether President Bush is capable of responding to this new mood, or whether he is to be swept away by the floodwaters of ideological intransigence.