The United States has been forced to reimagine itself this past month. So who better for the New Statesman to track down in his obscure mountain hideaway (no, not Bin Laden) than the man who has dedicated his life and writing to telling Americans their real, non-sanitised history: Gore Vidal. This is a man, after all, who knew and influenced the icons that defined 20th-century America. He was a close friend of more than one president (not forgetting that Eleanor Roosevelt urged him to run for elected office), was sucked off by Jack Kerouac, was attacked (both in print and to his face) by Norman Mailer, was a confidant of the Oklahoma bomber and Bill Clinton, and had to tell Tennessee Williams to stop trying to cruise Jack Kennedy. Now that the 20th century has truly reached its symbolic end, this is surely the ideal man to help us understand the new, battered America.

When asked if he is sleeping well, knowing that the US is in Dubbya's hands, he replies: "Let's just say I'm in a total state of insomnia." Unlike those who are rallying behind the president, Vidal retains his withering contempt for the man. His father was a "failure", and "when you get a bad gene pool, you don't necessarily enlarge it for high diving, if I may complete the grotesque metaphor". Bush has, in Vidal's eyes, failed to rise to the occasion since the attacks. "For those with an eye and ear for the false note, every note is truly false." It is not his mangled and incoherent words that appal Vidal, however. "No, I'm judging by actions. Obviously, requesting all those special powers pushes us even further along the path towards Hitler's Enabling Act of 1933. That is the worst that he could do."

Vidal sees the new powers that Bush has claimed to combat terrorism as completing the destruction of the Bill of Rights. "They're now going to lock up anybody they want to, silence anybody they want to. Those powers are now theirs, the dreamed-of powers for the state. The state will come out of this very, very powerful, and we the people, in or out of Congress assembled, will come out much weaker. That said, we glory in the fact that we are the United States of Amnesia. We won't remember a thing the next day." What has emerged is nothing less than "a police state. There's no euphemism for it . . . Now the attorney general can act against terrorism, which has never been defined. It's like 'un-German activities' under Hitler - what's an un-German activity?"

This fits into Vidal's wider history of an American republic progressively destroyed since the Truman administration, when the branches of government began to be owned and controlled by increasingly repressive corporations. It is this historical framework that leads him to damn the new American imperialism that is spearheading the invasion of Afghanistan. "I don't see that anything can come from a country that is so beautifully right that we would want to impose, either by suggestion or by fiat, our way of life on anyone else. And particularly so with the United States of America, the most corrupt political system on earth.

"How we dare even prate about democracy is beyond me. Our form of democracy is bribery, on the highest scale. It's far worse than anything that occurred in the Roman empire, until the praetorian guard started to sell the principate. We're not a democracy, and we have absolutely nothing to give the world in the way of political ideas or political arrangements. God knows, the mention of justice is like a clove of garlic to Count Dracula."

His scorn for what his homeland has become knows no bounds. He suggests, for example, that the United Nations would be "stronger if they kicked the US out of it: the US would be in quite a separate orbit". He is also unafraid to carry on drawing attention to the illegitimacy of President Bush. "At least five members of the Supreme Court should have been put on trial [for installing Bush] by the Senate, which is in charge of that under the constitution. Two certainly should have recused themselves. Clarence Thomas's wife was working to recruit people for the Bush administration; he should not have sat in judgement. Antonin Scalia's son was working for the law firm that represented Bush before the Supreme Court. That isn't done. Without those two, the decision would have gone for Gore."

All these criticisms could easily be used to portray Vidal as unpatriotic or, that laziest of cliches, "on the side of the terrorists". Yet he is plainly disgusted at the callous nature of the 11 September attack: "I am against the death penalty in general, and I am certainly against privatising it." He tries to see beyond the sensational pictures, both of the initial attack and the US retaliation. "My task is to try to get people to understand why something happens. I live in a country where everyone is trained from birth never to ask why. 'That man is evil - that's why he did it. That's the answer. He's evil.' Only with the fundamentally, totally uneducated could you get away with this sort of rationalising. I'm a true protest-ant, so I do protest at the ignorance. And that's my unpopular role, alas."

Vidal has been a fierce critic of America's support for Israel in the past, leading to predictable accusations of anti-Semitism. Does he feel that the attacks are the price the US is paying for supporting the Zionist cause? "Partly. But in Bin Laden's case, it's more complex . . . What triggered him was the Gulf war and the Saudi royal family allowing American troops to set up base . . . For Bin Laden, this was sacrilege. This was the holy land of the Prophet, and under no circumstances should the infidels be there . . . So I would think that he's far more angry with the royal Saudis than he is with George W Bush, or any Americans. We're just an outside instrument that is feeding heretical elements in his world."

He does not share the prevailing media depiction of Osama Bin Laden as a fanatic. "He has shown no sign of fanaticism in any of the stories I've been able to get on him: he seems rather secular. Which means that maybe he is part of a group. He seems more like a CEO to me, an organiser who raises money, does the salesmanship and so on, and then he has the crazies who go up there and run their aeroplanes into buildings."

Vidal displays a certain amount of detached admiration for Bin Laden's timing when he speaks of "the brilliance of it, to hit the moment that depression has just hit the US, and we're letting go hundreds of thousands of workers. Europe is about to experience the euro, which I think will be the biggest mess we've seen in years. I mean, what a moment of awful confusion that Osama decided to do his programme over Manhattan and the District of Columbia."

There also remains the possibility that Bin Laden was provoked. A Pakistani diplomat has claimed that the US threatened to enter Afghanistan to seize Bin Laden in July, which may mean that the World Trade Center attack was in fact a pre-emptive strike. Vidal has dedicated the past few years to showing that Franklin D Roosevelt knowingly provoked Pearl Harbor. So does he believe that the next great attack on American soil, 60 years later, may be similar?

"Well, that's what we went through when Kennedy got shot. Those of us who knew him and who knew Washington knew that he and Bobby had been trying to kill Castro ever since the Bay of Pigs. Our first thought was that Castro beat them to it - he killed him. And Bobby, who was then attorney general and remained so for a year, which meant he was in charge of the FBI, never investigated it. He didn't want to go near it, for fear that the Kennedy brothers would be involved. So that murder case was never investigated." So it's plausible that there was a similar provocation by George W Bush? "Perfectly plausible, yes."

There is just a hint - although Vidal doesn't state it explicitly - that this makes the attack much more understandable. "To understand why a man did it is a very important thing to do. Same thing with Timothy McVeigh [the Oklahoma bomber]. And if Castro had been behind the Kennedy killings, which he wasn't, one would have to say he had a motive. They kept trying to kill him all the time." So Bin Laden, in Vidal's view, is responding to US foreign policy.

The terrorist actions seem to have reinforced Vidal's isolationism. He has consistently argued that the US should withdraw from its commitments in Nato, Kosovo, the Middle East and other trouble spots. His vision is diametrically opposed to Tony Blair's of a "world community". Vidal dismisses Blair's plans as "positively viceregal", and impractical "unless you're going to work out a kind of blueprint for world government". He says that the Prime Minister thinks "the Brits would like to see themselves as a major player, with a great empire . . . You know, he's an actor, and that's a very good role. It's fun to play that and he has no responsibility at all. Dubbya's going to have to have the bombers go through the White House. Dubbya is really at risk now."

The best America can do, Vidal believes, is retreat. He believes that "elements south of the Russian border" are "susceptible to religious mania", and it "might be just as well that we are forewarned, and never provocative. Do not provoke. That's the message I really have to say about US policy. [The problem] is the endless provocation that the US goes in for - generally out of just sheer ignorance."

His homeland, he reminds me, has no sense of history. This may be Vidal's tragedy. He now lives in self-imposed exile atop an Italian mountain. He occasionally lobs intellectual grenades across the Atlantic: keenly polished ideas that expose the bland dishonesty of so much American culture. Yet even now, when the US might at last be forced to re-examine its identity, his countrymen are deaf to his erudite arguments. Perhaps, on second thoughts, this is America's tragedy, not Vidal's.