Terrorism has come of age and propelled the world into a new era whose potential horrors have as yet only been glimpsed.
In a couple of hours yesterday, the US faced the reality of the new kind of warfare that is set to replace in the national consciousness the threat of nuclear annihilation. Not since the Cuban missile crisis has this country felt so vulnerable. Senator Chuck Hagel called it "the second Pearl Harbour". President Bush called it a "national disaster".
There have been other serious terrorist incidents: Islamic militants bombed the World Trade Centre in 1993; in 1997 there was the Oklahoma bomb; two US embassies in Africa were attacked in 1998 within eight minutes of each other; and the USS Cole was last year crippled by a suicide attack in Yemen. But this is of a different order of magnitude. And this is a country that does not take casualties well.
Shock and grief will give way to rage and a determination to make those responsible pay. And US retribution will be terrible and overwhelming when it comes. Woe betide any government or organisation implicated. No quarter will be given.
The politicians have been warning about the new strategic reality, it is the rationale behind the new thinking which underpins President Bush's missile defence plans. With the end of the Cold War, the US has been redefining its perception of threats from the old enemies of Russia and China.
The new villains are the rogue states of Iraq, Iran and North Korea and the small bands of terrorist groups such as that of Mr Osama bin Laden, which have taken refuge in places such as Afghanistan, Yemen and Sudan.
Initially, speculation has focused on Mr bin Laden, with experts insisting that only three or four candidates in the world would be capable of organising such a co-ordinated attack involving suicide volunteers and simultaneous hijackings. Mr bin Laden's organisation is said to have issued generalised threats in the last few weeks similar to those ahead of the Cole and embassy bombings for which he is believed to be responsible.
Yesterday's claim by a spokesman for the Afghan Taliban government that it has Mr bin Laden under close supervision is not being taken seriously.
Mr Bush has spoken repeatedly of the new threat of terrorism and that traditional theories of deterrence can no longer work. He has found some echo for his fears among allies including Mr Tony Blair, even if they have had reservations about his remedy - the construction of a missile defence system that could cost as much as $120 billion and would involve repudiation of the Anti-Ballistic Missile treaty (ABM), possibly triggering a new arms race.
But the fundamental flaw of missile defence was even more basic. It was precisely the fact that it gave no answer to attacks of this kind, whether by conventional or nuclear means, when terrorists slipped under the country's guard to attack from the mainland. But yesterday's tragic events are unlikely to force a rethink; in fact they will enormously strengthen the hand of conservatives in the administration who will argue that it is better to have some defence than none.
The administration's unilateralist tendencies, even isolationism, are also likely to be strengthened after an initial global rallying of support and expressions of concern. The US's sense of itself as the global superpower will be reinforced, with conservatives in the cabinet such as the Vice-President, Mr Dick Cheney, and the Defence Secretary, Mr Donald Rumsfeld, arguing that the US must rely on its own resources to put its interests first. Anti-Islamic sentiment will be strengthened.
Yet such a course will lead the US in the medium term into worrying further clashes with allies and reinforce a drift away from Europe. Retaliation in the Middle East is likely to raise regional tensions. If the US does try to use the UN Security Council to legitimise such action, Ireland may face a difficult test of its neutrality. (Those in Ireland flirting with terrorist enemies of the US should expect an even colder shoulder from an administration already deeply troubled by such links).
Domestically, the Democrats will find it difficult to oppose once-controversial spending increases in defence and are likely to clear the way in the Senate for the 13 appropriations bills needed to implement next year's budget and which had promised to be extremely difficult. National tragedy has a way of rallying the nation and the aftermath of the crisis could well propel Mr Bush into a second term.
The attacks have already had economic consequences, rattling the stock markets and pushing the price of oil up sharply. The disruption caused by the closure of markets and businesses will be a significant setback, but in the long term the effect on consumer confidence will be most worrying at a time when the US economy needs all the help it can get. The cost of physical damage already runs to billions of dollars.
Above all, perhaps, will be the effect on the psyche of a people that has in this generation only experienced war on its television screens. A nation's sense of inviolability and invincibility has been punctured. Nothing will be the same again.