There were the two world wars, then the cold war. Sept. 11 was Day 1 of the new war yet to be named. America, the superpower, was rendered - momentarily, at least - superpowerless by an assault on its financial towers and military vitals. President Bush, who, in the first hours, was shuttled nervously by the Secret Service from Louisiana to Nebraska, finally emerged in the White House to assure a stricken nation that the government still functioned, and the president still presided.
Sept. 11 made a mockery of the nation's defense concepts. Missile defense against some rogue state, the Pentagon review of programs of mass destruction, the revamping of the defense structure to fight two - or is it one and a half? - regional wars, seemed suddenly like ancient history.
Asymmetric warfare, it dawned on us, could be a few zealots eager to die, deploying weapons no more sophisticated than knives to convert airlines into guided missiles.
The "how" of the terrorist siege of America may vary from a truck bomb attack on an embassy to an assault on a Navy destroyer and now to the exquisitely organized hijacking of airliners. What matters is the "who." This day of infamy - unlike Pearl Harbor - had no return address.
The weight of evidence, and the assumptions, point to the multimillionaire Saudi Arabian terrorist Osama bin Laden, who operates in a safe haven provided by the extremist Taliban rulers of Afghanistan. He had bragged, in self-promoting videotapes, of his blows against America. After the embassy bombings in East Africa in 1998, President Clinton went after him in the mountains of Afghanistan with missiles, but missed.
President Bush has promised to find those responsible for the terrorist assault and "bring them to justice." He has also promised retribution for "those who harbor them." We have heard that kind of language before, back with President Reagan, who said that terrorists "can run, but they can't hide."
That kind of language sounds faintly archaic. We are not simply on the hunt for a gang of thugs, but may be on the threshold of a wider clash, centered on, but not limited to, Afghanistan and the Middle East.
It is a war without borders, an unconventional war that will test the ingenuity of our military and intelligence resources.
It will also define the Bush presidency. Well-scripted invocations to character and values will not suffice.
President Roosevelt rose to the test of Pearl Harbor. Jimmy Carter failed the test of the Tehran hostage crisis. Mr. Bush faces a test that is, in many ways, more difficult.
Yes, America wants revenge. America wants to be assured that it is still No. 1. But more than that, Americans want to feel that they are safe in their own country. That is a formidable task for the president.
Daniel Schorr is a senior news analyst at National Public Radio.