Perhaps the only thing about President Bush's first term that everyone agreed on was its turning point: Sept. 11, 2001.
Now, exactly four years later, the president's second term has also come to an early defining moment: Hurricane Katrina.
In 2001, the Al Qaeda attacks on New York and Washington took nearly 3,000 lives and terrorized America's two most symbolic cities. They destroyed the World Trade Center, a prime icon of American economic power, and heavily damaged the Pentagon, the seat of U.S. military might. Whole industries shuddered; the economy slowed.
The psychological blow to the national consciousness was staggering. But it also lent itself perfectly to the president's counterpunch. His resolute demeanor and decisive response to the attacks united the nation and made his presidency.
It was his finest hour. It helped Republicans recapture control of the Senate in 2002 and, shown again and again on TV, it carried him to re-election in 2004.
Much is different in the current crisis, however, starting with the disaster itself. This time, we have no symbolic targeting, no evil mastermind and no prospect of revenge. This time, it was what insurers call an act of God.
We could also call it a catastrophic coincidence of nature — meteorological and human. A storm of historic size and fury struck the most vulnerable of our coastal areas. Just as important, this uncontrollable cataclysm was preceded and followed by an aggravating cavalcade of human error.
The folly began centuries ago with the growth of a city where everyone knew a major storm surge could be fatal. But it also continued into our own golden age of miracle engineering, when political decision-making neglected local levees and let coastal defenses erode.
When the levee broke, the waters rushed through, and another phase of human error began. The people of the city's poorest quarters (more than a quarter of New Orleans lived below the poverty line) were left trapped and desperate. The various governments tasked with their safety and protection failed them.
The ensuing death, suffering and lawlessness were played out on cable TV news day and night for a week — a spectacle witnessed worldwide. China offered us doctors. Venezuela offered free fuel for the poor. Third World nations offered cash. Still more humiliating than any of these offers was the realization that we needed the help.
On Sept. 11, 2001, America suffered the chagrin of being ambushed. But that anger could become righteous, and we could turn it outward upon the conspirators.
In the current instance, we have no one at whom to rage but ourselves. We are reduced to factions, endlessly blaming each other.
After a few months, these differences could add up to a political lesson quite distinct from those learned in the wake of Sept. 11.
Bush may not descend into polling hell because of Katrina, but he may not get much of a bounce from the rally-round-the-leader effect, either. In 1995, President Bill Clinton saw his approval score climb dramatically after the Oklahoma City bombing. In 2001, President Bush's approval soared to 91 percent after the Sept. 11 attacks (it had been 51 percent).
Much else has changed since that Tuesday in September four years ago. Mr. Bush's approval in the Gallup Poll reached an all-time low of 40 percent 10 days before Katrina. He was doing a little better in some other pre-storm polls, but he was at his lowest point ever in all of them.
In 2001, Mr. Bush was a new president, enjoying his contrast to his predecessor, the sullied Mr. Clinton. Now, suddenly and visibly, he seems an aging leader. Instead of standing tall and addressing a hushed Congress, he turns to his father and even to Mr. Clinton for help.
The Katrina crisis intrudes on America's history at a complex moment for the nation's economy and the world's affairs.
Even though U.S. unemployment had fallen below 5 percent before the hurricane, Americans are dissatisfied. Household income has stagnated for five years in a row, the first time that's happened. Health, housing and education costs are up substantially. The percentage of Americans in poverty rose again last year, and now the Gulf Coast region has lost hundreds of thousands of jobs and billions in economic activity. The rate of growth in the economy is expected to slow this year and next.
Meanwhile, gasoline prices are at nominal highs (approaching records even in constant-dollar terms) and shortages have begun to appear. The president says he can't control the markets, and he snaps his fingers in derision at the idea he could lower prices. But 70 percent to 75 percent of Americans tell pollsters they think the government should be doing more to do just that.
And amidst all these worries there remains the ache of the war. Ask the people in Louisiana why they did not get the National Guard help they needed in August and they talk about how many of their guys are in Iraq. Secretary of Defense Donald Rumsfeld says the war was not a factor, and that the Pentagon has plenty of people for both tasks.
In the weeks ahead we will see how persistent the Katrina crisis proves. Sept. 11 has become not just a memory but a permanent part of our lives. Katrina brought not just flooding and death but displacement on a scale without precedent. How long will these human beings suffer, and how will they change the communities to which they are sent?
The experiences awaiting us in the months ahead will not be like those of 2001 and 2002. And neither will the political fallout be the same.