November 1976. It is 3am, but despite pleas from my mother, I still won't go to bed. I am 16 years old and I am gripped. Peter Snow is running backwards and forwards on BBC1 as bits of his map of the United States turn blue and red, and the world begins to realise that Jimmy Carter, a peanut farmer from Georgia, has triumphed over Richard Nixon's successor, Gerald R Ford.

American elections have always fascinated me. So deeply ingrained are my train-spotting instincts in this domain that I can tell you the electoral college voting numbers for every US state. But I have never cared about the outcome of any US election as much as I care about this one.

Why? Because I am a Christian who is terrified at the prospect of a de facto American theocracy becoming entrenched within the inner circle of Bush's Oval Office. It is enough to make Montesquieu turn in his grave. No country has gone to greater lengths than the United States to develop constitutional checks and balances and to keep religion and politics in separate spheres. It learned the lessons of Europe's savage wars of religion. The slow re-emergence of the "one law, one king, one faith" at 1600 Pennsylvania Avenue should worry us all.

Consider this story from November 1998. It was some weeks after George W Bush's landslide re-election as governor of Texas. Bush was at a packed First United Methodist Church in Austin and wondering whether to run for the White House in 2000. He leaned back in his pew to listen to Mark Craig, one of his favourite preachers. The pastor kept his congregation enthralled with a tale about Moses.

"Moses almost ducked out," said the minister. "He tried every way possible to tell God that he was not worthy to lead the Israelites." Craig paused, then said: "Our nation is starved of honest leaders."

In his autobiography, A Charge to Keep (after a hymn by Charles Wesley), Bush dwells greatly on that moment. "That sermon spoke directly to my life and my heart. He was speaking to you, my mother told me later on. And the pastor had prodded me out of my comfortable life as governor of Texas and towards a national campaign." There is no mention of clouds parting and heavenly angels rejoicing, but the account gives an eyebrow- raising insight into the president's mindset.

Having spent months researching his religious faith, I have not the slightest doubt that Bush believes God chose him to lead the Creator's "favoured" country through the uncertainties of the post-9/11 world. As he told Congress in his January 2003 State of the Union address, two months before military operations began in Iraq: "This call of history has come to the right country . . . The liberty we prize is not America's gift to the world, it is God's gift to humanity."

There is nothing new about an American president wearing his religious heart on his sleeve. It's a sine qua non of successful electoral appeal, especially in the Deep South. But contrast Bush with Jimmy Carter. The peanut farmer was a man of intense private religiosity and devotion, but the more he dwelt on God and the deity's transcendence, the less comfortable he felt about identifying specific national political and military objectives with a sense of divine mission.

Even Bush's fellow Christian evangelicals are worried. Take Reverend C Welton Gaddy, a man of impeccable Bible Belt credentials (born in Louisiana) and now head of Washington's Interfaith Alliance. "Are Jews and Muslims hurt or offended by the specific Christian language the president uses in his speeches?" I asked him. "Some are offended, but others are just frightened," he replied. Gaddy said he was proud that an evangelical Christian was in the White House, but Bush's identification of America's cause with God's plans for the world was simply too much. "Any time you see a shotgun wedding between religion and politics, bad things happen," he said. "Illegitimate children get born. To be honest with you, it frightens me to death."

It is hardly surprising that, as a Catholic, I do not see eye to eye with Bush's own brand of Christianity. However, what disturbs me more than anything else is a drift towards what can only be described as idolatry.

Yes, idolatry. A strong word, I know, but let me single out a Bush speech to illustrate the point.

On the first anniversary of 9/11, the president's speechwriters chose Ellis Island and its picturesque backdrop of New York Harbour for his address to the nation. "This ideal of America," said Bush, "is the hope of all mankind. That hope drew millions to this harbour. That hope still lights our way. And the light shines in the darkness. And the darkness will not overcome it." It is a pity that St John did not appoint an estate to sue on his behalf. The president and his team had raided the prologue to the Fourth Gospel, perhaps the most beautiful words in the New Testament. Bush had, in effect, equated the US with Jesus. The world's most powerful nation, it appears, really is the agency through which God will manifest himself and reveal his plans to the world.

Cynics would argue that Bush does not believe a word of all this and neither does his evangelical speechwriter Michael Gerson. That it is merely a handy political strategy: you lace each speech with a few choice biblical quotes and trigger off conscious or subconscious approval from born-again Christians, who comprise more than 40 per cent of Americans, according to a recent Gallup poll. Even that would be an indictment of Bush and his team, but for once in my journalistic career, I will not impute base motives. No, on the evidence of dozens of conversations and hours of reading, I think he really means it.

One of those conversations was with Stephen Mansfield, author of The Faith of George W Bush. I knew he was an important individual because his Christian credentials had persuaded Bush's advisers to allow him unparalleled access to the inner world of the faith-based presidency.

Scores of journalists have been refused access to the key characters from the Bush faith story: the countless preachers, such as Billy Graham, who have shared their biblical insights with the president since his conversion at the age of 39. Yet that did not include Mansfield; he had the keys to the Oval Office. So how did he see this tendency to equate the priorities of the US government with the will of God?

"Well, if I am honest," he said, "that is one part of the president's approach that has to be kept a bit in check." What about that bastardisation of St John's Gospel and all that light and darkness stuff? There was a silence on the phone. "Yeah," Mansfield resumed, "you've got a point there."

Such candid reactions are not common. Back in the summer, Bush visited Lancaster County in Pennsylvania to meet a group of Amish farmers. A number of those attending reported that Bush had said to them: "I trust God speaks through me." Journalists called the Bush press team wanting to know more, but all they ever got was a denial of these precise words. In their place, they were given a more anodyne but still politically useful sentence: "[Bush's] faith helps in his service to people."

A number of those who monitor the comings and goings of the Bush inner sanctum record an increasing disregard for factual evidence and a growing emphasis on faith-based instinct. In the New York Times, Ron Suskind recorded a meeting with a senior Bush adviser:

The aide said that guys like me were "in what we call the reality-based community", which he defined as people who "believe that solutions emerge from your judicious study of discernible reality". I nodded and murmured something about Enlightenment principles and empiricism. He cut me off.

"That's not the way the world works any more," he continued.

"We're an empire now, and when we act, we create our own reality. And while you're studying that reality - judiciously, as you will - we'll act again . . . We're history's actors . . . and you, all of you, will be left to just study what we do."

Looking ahead to the prospect of much more of this during a Bush second term, Suskind quotes another aide. "When it gets complex," the aide said, "he seems to turn to prayer or God, rather than digging in and thinking things through. What's that line? The devil's in the details. If you don't go after the devil, he will come after you."

As I ponder the election of the next president and the prospect of four more years of George W Bush, I am left with two chilling thoughts. First, here is a man who sincerely believes that the fight against al-Qaeda resembles a Manichaean war of all that is good against all that is evil. His opponents may want to institute an Islamic theocracy where notions of law, God and the state overlap as one. But the mounting evidence is that Bush and his team of neoconservatives have been involved in precisely the same transformation themselves since 2000, albeit more covertly.

As Bruce Bartlett, a former Treasury official who worked with George Bush Sr, has said: "He understands them because he is just like them."

And second, while Osama Bin Laden does not have a time limit on his ambitions, there is every possibility that, if they are re-elected, Bush and his born-again advisers will conclude that they have four remaining years to bring God's plans for the world to fruition. I have never previously prayed before an election but, on 2 November, I might just break with that precedent.

Mark Dowd is a journalist and former Dominican monk. Earlier this year, he presented a three-part documentary on Channel 4, Children of Abraham