Armour, however, is no protection against flood. Disasters usually distract critics, silence malcontents, flatter leaders, and improve presidents' ratings. Not this time. Katrina could be the storm that finally scatters Mr Bush's strangely tenacious following.
It is not just that he has handled the crisis badly. His first response was a bemused look, reminiscent of his mental paralysis at the news of 9/11. He then committed a terrible blunder, telling disaster victims to "take personal responsibility". The individualist message was miscalculated, offensive to the altruism that disasters always ignite. Next, the President seemed to think that it was more important to stop the looting than to save lives. His gaffes don't end. In storm-torn Biloxi on Friday, he referred two distraught women, who collapsed in his arms, to the Salvation Army shelter.
Not even Canute could stop the waves, and the ludicrous inadequacy of the coastal defences was a long-standing scandal that the region's state authorities, not just the federal government, had neglected. But the victims grew angry because of the slowness of the President's response, the inadequacy of federal funding, the shameful facts - so reminiscent of 9/11 - of federal agencies' indifference to warnings, and the helplessness of the government in the face of growing chaos and suffering. Mr Bush became a new Nero, fiddling while New Orleans flooded.
The terrible truth is now out: the government cut flood prevention funds to pay for war. So far, the question hasn't been asked, but you can see it between the lines in the press and sense it trembling on millions of lips: if the government can find money and manpower for Baghdad, why not for Biloxi? On Friday, five days after the disaster, Congress voted $10bn (£5.4bn) of relief aid. Nobody around the Gulf Coast feels grateful. "Not before time," they say.
Countless unbiased journalists have reported how non-government agencies, charitable institutions, and philanthropic individuals took care of Katrina's victims, while the authorities' efforts seemed invisible - as if the whole operation were a gruesome exercise in privatisation. It took five days for the circling helicopters to rescue survivors, five days for the National Guard to arrive with food and water for those stranded in New Orleans. Americans are bound to make a so far unspoken, but glaringly obvious, comparison with the resolve the government shows when it tackles the President's real priorities: war, power, petroleum, environmental profligacy.
For deeper reasons, the present crisis is particularly challenging for Mr Bush. Like his counterparts in al-Qa'ida, Mr Bush is a fundamentalist, with beliefs undisciplined by science or reason. His faith obliges him to take literally the story of Noah. He sees the world as a divine arena, where there is no evolution without design. The more he bangs on about prayers for the victims of disaster, the more he invites the obvious ripostes. On the one hand, hostile fanatics claim that Katrina was a ray from God's zapper, shot to immobilise a limb of the Great Satan. On the other, the secularists sneer with the usual taunt in the face of disasters: "Where is God?"
The President is not theologically supple enough to answer effectively. Maybe this is why he looks bemused: is he still sure of having his God's approval? The next time he goes back home on the range, will the cowboy-president still think Ol' Mother Nature is his friend?
Under the "yah boo" exchanges of religious and irreligious zealotry lurks a serious issue. Mr Bush has staked his reputation on eco-scepticism. He doesn't believe in global warming. He shelves environmental projects. He despises Kyoto. He dismisses predictions that nature's revenge will swamp human arrogance. After Katrina, Mr Bush's appraisals of environmental threats look worthless.
Bad news for the disaster victims is bad news for the President. And the bad news keeps coming. After days immured in the fetid refuge of the Superdome in New Orleans, thousands of hungry, filthy, critically dehydrated, penniless, virtually shirtless refugees - most of whom happened to be black - were stranded for hours in buses which the police turned away from an overcrowded emergency camp in Houston.
In the foul, corpse-strewn, sewer-like streets of New Orleans, the crisis has entered a new phase. The psychology of altruism has evaporated. To begin with, it was "Women and children first". Now it's "Every man for himself", in a horrifying caricature of Mr Bush's philosophy of individualism. Looters kill for the spoils of catastrophe, as predatory as the roaming alligators that have come in from the wetlands. Estimated numbers of dead keep rising.
A second disaster looms: the long-term health of people who have been dehydrated, starved, deprived of medication, and marooned in cities that have become insanitary swamps. By Friday, the relief effort was just beginning to look organised - but the horror stories and recriminations will drive the successes out of the news for weeks to come. They multiply hourly: abandoned prison inmates leaping to their deaths after days without water; doctors overcome by the stench in hospitals where the lavatories can't be flushed; hundreds dying, while waiting for a rescue vessel that is anchored in red tape.
The rest of America has rallied. Despite the Lone Ranger rhetoric of freedom, amazing reserves of solidarity bind US society. It starts with neighbourliness, swells into civic pride, and becomes patriotism. My university opened its classes to students displaced from the Gulf Coast, helping to lead a similar movement around the nation. Schools where refugees have taken shelter have done the same. Disaster relief has become a national, rather than a federal, effort. The government is outdone, engulfed and isolated by a wave of sympathy for fellow citizens in distress.
Regional authorities in the Mississippi Delta who failed to forsee the tragedy are, for the moment, escaping most of the resentment. Governor Hailey Barber of Mississippi disarmingly confesses failure while wanting to make up for it. His popular touch comes naturally, where the President's always seems scripted. People believe Mr Barber when he promises that "we're gonna hitch up our britches". Mr Bush, meanwhile, keeps promising a better future, when what the victims want is present relief. His uneasy optimism seems reflected in the gleaming eyes of fat-cat friends, already prowling around for prospective reconstruction contracts.
When the terrorists struck on 9/11, Mr Bush could make any number of mistakes, and still gain in popularity, because there were aliens on hand to hate. He could launch and mismanage wars with impunity, counting on the electorate's fidelity in the face of the foe.
This time Mr Bush cannot rail against God or, with his environmental record, make an enemy of nature. He cannot bomb the sea or invade the wind. God and nature are on the same side; and they no longer look like America's coalition partners. Even in the context of a natural occurrence, where there is no real enemy, people still need to hate and long for vengeance. Slowly, inexorably, with a chilling uniformity, the accusing gazes are focusing on the White House.
Felipe Fernández-Armesto lectures at Tufts University, Massachusetts, and is Visiting Professor of Global Environmental History at Queen Mary College, LondonReuse content