Until the collapse of communism, America's experience as a great power had been of a world in which there was always (as she saw it) one great evil in the universe, committed to her total destruction. She stood for more than national self-interest; she stood, she believed (and often rightly believed), for the forces of good. A Manichaean universe in which America captains the Army of Light while in the surrounding dark 'the hosts of Gideon/Prowl and prowl around', characterises her whole memory of power.
That is not surprising. The Founding Fathers were (like fundamentalist Muslims today) in flight from what they saw as a fallen world. God, or destiny, had commanded America to start again. Being the New World was more than a matter of dates; it was a matter of innocence too.
It follows that the short period between 1989 when the Berlin Wall came down, and 2001 when the World Trade Center followed it, was a novel and perhaps unsettling experience for America. The innocence of the early post-Revolution years may have been sacrificed to almost a century's involvement in world affairs as a boss nation, but if she had bloodied her hands, she had bloodied them wielding the sword of light. Against whom should the armour of righteousness be put on next?
A psycho-political analyst might conclude that here, after 1989, was a great national collective unconscious in urgent search not of a God - He had been located on America's side - but of a Devil in which it was possible for modern Americans to believe.
September 11 was not a post-Freudian allegory, of course. It was a reality whose perpetrators were not only wicked but powerful - or so it looked from the mayhem they created. But beyond being real the event was also perfectly placed as a national myth: an explanation, a clarifier, a catalyst permitting America's perception of the era to re-form around a new version of the dualism she inwardly craves. Of course one voice in America's head said, 'This bewilders us'; but another said, 'Ah - so that's where the Devil's hiding.'
It follows that as a great national idea the War on Terror is likely to take root and flourish, almost regardless of whether it fits the emerging facts. The viability of this theory will prove remarkably resistant to lack of supporting evidence.
Seeking a template to guide us through the Through the Looking Glass years ahead, we could do worse than reread the history of an era which, though attributed to one opportunist senator, drew its vigour from a comparable national idea: McCarthyism. As England's fear of a Catholic plot spawned Titus Oates, so the fear of un-American activity needed and therefore spawned Senator McCarthy. Ellen Schrecker's The Age of McCarthyism: A Brief History with Documents (Bedford/St Martin's) provides a useful textbook.
The McCarthyite view had (as Schrecker points out) one undeniable advantage over, say, fear of witches in Salem: communists existed. The Soviet Union was dangerous and did hope to infiltrate America. Those who suggested that McCarthyites overstated the fiendish intricacy of the Soviet web were therefore easily dismissed as being at best naive, at worst complicit. I remember my family being called communists in southern Rhodesia because my mother campaigned for African education; we were never communists, but she confided in us that she did have doubts about a couple of fellow-campaigners; Moscow did give aid and comfort to anti-colonial movements in Africa.
In the same way, none can deny that al-Qa'eda exist, that their aims are horrible, and that they are probably still plotting. We who retain (I hope) an open mind as to how deep, how wide, how numerous and how sophisticated that organisation may be are easily wrongfooted by the haunting image of burning skyscrapers. A picture has become almost an argument. But if Schrecker's account is any guide, there are tell-tales for which we should stay alert:-
1) The imputation of guilt by association. Watch for the use of terms like 'linked', 'possible links to', to beef up a thin story. Slyly employed, such words suggest a hard link where only a soft association exists. Recently I heard an even craftier trick: someone was described as 'linked to al-Qa'eda' when (it emerged) that the speaker meant other people had speculated on a link; the suspect was thus 'linked' (by other people) to al-Qa'eda.
2) Talk of 'front' organisations. They may be. Or they may turn out to be sympathetic but distinct. In this sense the Countryside Alliance is a front for the Conservative party, or vice versa.
3) The slither from sympathy to 'sympathiser'. I once wrote that we should try to understand the grievances motivating terrorists, so I may find myself called 'an al-Qa'eda sympathiser'. Millions of Muslims may. To support anything al-Qa'eda is presumed to believe can make you 'an al-Qa'eda supporter' - or 'apologist'.
4) News of the capture of 'key' figures. Watch for words like 'ringleader', 'linchpin', 'henchman', 'insider', 'senior', 'organiser', 'piece in the jigsaw' and 'breakthrough'; they are almost meaningless and therefore unrebuttable. Be sure that no arrest will be described as being of a junior, peripheral or unimportant outsider. An impression is created of an emerging picture as the searchlight picks from the shadows new and menacing faces.
5) Big-sounding stories which mysteriously vanish. If the chap who wanted to explode his shoe, or the chap who tried to take a gun on a flight from Sweden, and various other people with beards, turn out to be nutters, no-hopers or loners rather than insiders, such news will receive a fraction of the coverage that their apprehension achieved. That Ramzi Binalshibh (seized in Pakistan) was 'close to' the al-Qa'eda 'leadership' was splashed across front pages. That (as it transpires) he is fairly small fry is only now dribbling out.
6) 'Security' as a justification for the apparent death of a story. Is anything really being learned from those people in cages in Cuba, initially described as 'crack troops' or 'advance guard'? Silence. Ah, but the Pentagon could hardly tell us what it is learning from them, could they?
I took down (from the radio) this: 'Al-Qa'eda are said to have banking resources in over 200 countries.' This is more countries than there are in the world, so my suspicions were aroused. 'Are said' by whom? What are 'banking resources' - bank accounts in the name of the al-Qa'eda organisation? Hardly. In whose name, then? 'Front' organisations? People 'linked to' al-Qa'eda? Slowly the assertion dissolves. There are people in a number of countries who may put resources at the disposal of al-Qa'eda and who have bank accounts. Well, yes.
Al-Qa'eda may be every bit as formidable as even the most alarmist commentary suggests. But if it is not, this will not now stop America from persuading itself otherwise.
Matthew Parris is a political columnist of the Times.