President Bush must be feeling awfully lonely in the White House this weekend. Things are bad enough for him – battered by the war in Iraq, rock bottom in the polls – without last week’s sudden departure of his friend of 34 years, his chief adviser and the man behind his rise to the presidency.

Karl Rove, the guru who crafted George W Bush’s two election victories and boasted the title The Senior Adviser to the President (note the definite article), had once envisaged a new America run on conservative ideals for a generation, based on a mighty coalition backed by the religious right.

Bush deferred utterly to Rove, hailing him as the Boy Wonder and the “architect” of his victories. In private he dubbed him Turd Blossom – after the Texan flower that grows out of horse dung. So instrumental was Rove to White House policy that observers called him “Bush’s Brain”.

When the two men parted last week on the White House lawn, it was like a lovers’ farewell. Bush, red-nosed, granite-faced, could barely control his emotions as he said: “Karl Rove is moving on down the road. And so I thank my friend. I’ll be on the road behind you here in a little bit.”

Rove – a well known blubber – was even more upset, choking back the tears as he said how wonderful it had been to help “a man of farsighted courage put America on a war footing and protect us against a brutal enemy in a dangerous conflict that will shape this new century”.

He has ostensibly left the Bush operation for that old reason: to spend more time with his family – his second wife and 18-year-old son in Texas. The real reason for his departure was that he has lost his magic touch and the Republicans have lost the knack for the one thing they were good at, thanks to Rove – winning elections.

Rove’s disputed involvement with the Valerie Plame affair – when the senior Republican official Scooter Libby was jailed for identifying a CIA spy – did not help matters either. It became clear that the Turd Blossom was no longer blooming.

When I met him, shortly before his departure, he bore no signs of the impending rupture. Over lunch he was very much at ease running the show. He variously jousted and joshed, basking in the glow that radiates from that massive brain and his all-powerful boss. An awestruck silence fell on the room as he bustled in, unassuming, ungrand, but all the grander for it.

In the flesh, this master image-sculptor does not cut much of a prepossessing figure. To start with, there’s a lot of flesh – Rove may be Bush’s Brain; he is certainly not Bush’s Body. The belt that holds up the trousers of his cheap suit bites deeply into the lower slopes of a large, overarching belly. One former colleague fondly recalled how Friday was ice-cream day, when Rove bought ice-cream for the whole office. He and his devoted secretary would snack all day on the constant supply of sweets that she kept on her desk.

Rove is distinctly ungroomed. His remaining strands of white hair float above his pate in a wild halo – the oddest comb-over I’ve ever seen – leaving a sort of hatmark where his hair furls away from the scalp. He admits that he is no pin-up. He says of his time at high school in Salt Lake City: “I was the complete nerd. I had the briefcase. I wore Hush Puppies when they were not cool. I was definitely uncool.”

And yet, unlike most political nerds, Rove has immense charm and presence, his cheerful, confident smile and button nose the little anchor to his big face. He relishes tricky questions. He opened each answer with a cutesy but engaging anecdote, swiftly followed by a volley of nerdish statistics to back up the Bush administration’s record.

Before making a point about wonky health issues, he said, in his down-home, Nevada, folksy accent: “Mah daddy died on Medicaid [the basic American health provider] and it shocked me. Now the average benefit is $11,890 a year. My mother-in-law gets exactly that. I wish she didn’t but . . .”

Yet like all top spin doctors Rove prefers to stay out of the spotlight himself. Over the years he has given precious few interviews and, in those that there are, more quotes appear about him from other people than from the man himself. He is artful at deflecting questions preferring to riff, say, about “how in the real West Wing the lighting is nowhere near as flattering, there are no glass walls and a lot less takes place in the hallway”. He is careful always to show his boss in a good light, saying that his friendship with Bush thrives on banter: “Ours is rather childish – and he gets the best of me every time.” Really?

I saw myself how Rove’s smile can turn with lightning speed to a snarl. At a lunch I attended with him and some other journalists, one of the hacks accused the Bush administration of not being conservative enough in its domestic policy.

“You don’t know what you’re talking about,” said Rove, his eyes roving round the room to meet ours, all bonhomie gone in an instant. “It’s so easy for journalists to look at any policy, decide it doesn’t fit in with their preexisting rules of what’s conservative or not, and then say we’re going soft. It doesn’t work like that.” The froideur was total. Then, snap, just like that, Rove turned back to his old genial self for the remainder of the lunch.

I wanted to know what the master of compassionate conservatism and wily election warrior reckon to our own Conservative challenger – did he think David Cameron had a chance of beating Gordon Brown?

“It’s going to be difficult,” Rove told me. “They haven’t got the religious backing the way we did.” So how did the Republicans change people’s minds about the party?

“It’s about being for something as opposed to against something. Conservatives find it very easy to be against something. We’re against slovenly behaviour. We’re against welfare rolls. We’re against people being on the dole. We’re against this bad thing and that bad thing. Instead, what we should do is find ways to herald things that are positive. We’re for ending dependency on government. We’re for helping people to achieve the best that they can be in life.”

Steve Hilton, Cameron’s ideas guru, could certainly learn a thing or two from Rove.

At the height of his powers, Rove assembled a bag of electoral tricks that make Peter Mandelson and Alastair Campbell look like relics from the Pathé news age. Rove was responsible for couture Republicanism, salami-slicing the conservative message and tossing choice morsels at particular groups.

The most fertile targets in 2004 were the Bible-Belt voters, courted with a strong Christian message wrapped up in pro-life, antigay marriage mood music.

His genius was for courting floating voters. Say you were pounding the rubber steps on the office gym StairMaster at eight in the morning. Rove was there to catch you. He and his team worked out that lots of voters, particularly upmarket ones, are not at home for the morning or early evening network news. So the Bush campaign pays for Republican advertising on closed-circuit gym channels at peak hours.

Rove’s sophistication took on board all the latest technological wheezes. The Republican news machine – the so-called “political shop” – used bloggers, lobby groups and radio hosts to push home the message. Google Earth satellite pictures were employed to get the quickest possible routes for on-street canvassing. Republicans took advantage of YouTube to target teenagers – recently they posted antidrug videos on the site.

However, while Rove was great at winning elections, he and his boss were not so good at getting things done. Iraq is the great spanner in the Bush works – fine in conception, inept in transaction. On the domestic front, where Rove had so many plans, things have also stalled. The attack on America on 9/11 meant that, whatever the Republicans wanted, they could get – Bush’s approval ratings soared.

Rove deftly used security issues to damn the Democrats. As he puts it: “Conservatives saw the savagery of 9/11 in the attacks and prepared for war; liberals saw the savagery of the 9/11 attacks and wanted to prepare indictments and offer therapy and understanding for our attackers.” Six years on and Iraq blots out most of Bush’s domestic record but, all the same, few of Rove’s ambitions were fulfilled. Hurricane Katrina did not help – it was Rove who said that Bush should not land in Louisiana shortly after the disaster, leaving him hanging, ineffectual, mid-air, over New Orleans.

If anything, the complete domination of American politics orchestrated by Rove also brought him down. His utter confidence and bombast alienated Democrats, the electorate, Republicans even. Recently Bush has become aware of the problems attached to his consigliere. When he tried to get his immigration policy through Congress this spring, he made it clear that Rove would not take part in the negotiations. As Dick Armey, a former Republican congressman, said of Rove’s dealings with Congress: “You can’t call her ugly all year and expect her to go to the prom with you.” Rove, now 56, will not disappear from the political scene altogether. He is to write a book about his three decades with Bush. And he will remain a significant Republican operator for next year’s presidential election. But his fall will be a hard one – he has lived and breathed the Republican party since his childhood in Nevada where he was deserted by his biological father and took on the name of his Norwegian-American stepfather, a mineral geologist. His mother committed suicide in 1981. No great student, he attended three universities and graduated from none of them.

What were never in doubt were his Republican credentials. At the age of nine he decided to support Richard Nixon and, as soon as he flunked out of Utah University, he became head of the College Republicans, a powerful student body. From the late 1960s onwards he was moulding himself as the ultimate election winner, setting up his own direct mail firm to back Republican campaigns. Since then he has been the primary strategist for 41 statewide, congressional and national Republican campaigns; he has won 34 of them.

He first met Dubya in 1973 while he was working for Bush’s father. “Huge amounts of charisma, swagger, cowboy boots, flight jacket, wonderful smile, just charisma – you know, wow,” he says of their first encounter.

In 1989 he was encouraging Bush to run for Texas governor. By 1999 he was working full-time as Bush’s chief strategist for the presidential bid – a year later they were in the White House.

As the architect of Bush’s dream strolled off into the sunset last week, he left behind him an increasingly embattled figure in the White House. For Bush, the shadows really are drawing in.

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