Shawn Adolf and his cousin Tharin Gartrell fancied that 28 August, 2008 would be a good day for the next president of the United States to die. They had the guns – Gartrell was later caught with a Ruger Model M77 Mark II bolt-action rifle with an attached scope and bipod, and a Remington Model 721, also with a scope. They were believers in a radical white supremacist ideology that gave them the motivation they needed to risk their own lives, if necessary, to prevent a black man from entering the Oval Office. (Or, as a friend reported Adolf as saying: "No nigger should ever live in the White House.")

And they had at least the outlines of a plan. They checked into the downtown Denver hotel where they believed Barack Obama was staying, and talked about the ways they could try to gun down the Democratic nominee on the day he was due to accept his party's nomination at an outdoor sports arena before an adoring crowd of more than 70,000 people.

Like many assassins before them, both the successful ones and the idle fantasists, Adolf and Gartrell took their inspiration from popular culture. They considered hiding a rifle inside a hollowed out television camera – an idea they borrowed from the Kevin Costner-Whitney Houston vehicle The Bodyguard. (It is also similar to the way al-Qa'eda operatives posing as a news crew assassinated Ahmad Shah Massoud, the leader of Afghanistan's Northern Alliance, on 9 September, 2001, but it is far from clear whether Adolf and Gartrell had any notion of this.)

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They toyed with the idea of hitting Obama from as far away as 750 yards, using one of their high-powered rifles; according to their friend Nathan Johnson, who may or may not have been part of the plot, they had in mind the conspiracy theory that President Kennedy was not shot by Lee Harvey Oswald from the sixth floor of the Texas School Book Depository building, but rather by professional assassins stationed on the "grassy knoll" above Dallas's Dealey Plaza.

None of these plans was ever remotely realistic, however. Adolf and Gartrell may have had some fearsome weaponry, and a vague affiliation with a white supremacist biker gang called the Sons of Silence, which disavowed them the moment they were arrested. But they were also rank amateurs living in a crystal methamphetamine-induced haze of paranoia and race hatred. (One can't help thinking Adolf's name went to his head, at least a little, as he fingered the swastika ring on his finger.) They had no clue how to circumvent the security surrounding Obama – prosecutors who examined their plans laughed them off as ludicrously naïve. And they couldn't even figure out what every half-interested member of the press corps knew, that Obama was not staying at the Hyatt Regency, the temporary HQ of the Democratic National Committee, but at a different hotel altogether.

Four days before Obama's acceptance speech, Gartrell was pulled over for drunk-driving in the Denver suburb ' of Aurora after a patrol officer spotted his rented Dodge Ram truck swerving erratically, and the whole plot, such as it was, fell apart almost instantly. Certainly, the officer found plenty inside the truck to sound alarm bells – the two high-powered rifles, a silencer, a bulletproof vest, camouflage clothing, and three fake identification cards. But it was also clear that Gartrell was high on meth as well as drunk. The truck contained enough drug-making equipment to be considered a mobile meth lab.

Gartrell ratted out Johnson and Adolf almost as soon as he was taken in and photographed for his singularly striking mugshot. (With his bleached blonde hair, heavy silver earrings and pierced lip, he looks like the neo-Nazi from central casting.) Johnson was in the room at the Hyatt Regency, and wasted no time in talking himself – insisting he had no idea about any assassination plot while almost simultaneously telling the world Adolf was planning to "go down in a blaze of glory" and take Obama with him.

Adolf was a tougher proposition, the only one of the three with a serious criminal record, including burglary, forgery, drugs and weapons raps. At the time of his arrest he was wanted on eight outstanding charges and had recently skipped out on a $1 million bail payment. He was staying at a different hotel in the Denver suburbs. When the police arrived, he jumped out of his sixth-floor room on to the roof of the hotel kitchen four floors below, then jumped again to the ground, breaking his ankle as he landed. He didn't make it far. He, too, was found to be high on meth. When asked why he was wearing a bulletproof vest, he said he was convinced someone wanted to kill him.

We will no doubt learn more colourful details about the trio of would-be assassins when their trial begins this week. Intriguingly, though, they are being prosecuted on drugs and weapons charges only. Their prosecutor, Troy Eid, has said he is absolutely confident the "meth heads", as he calls them, never posed a risk to Obama or anyone else.

Not everyone is happy with this decision. After all, marginal people have hatched assassination plots before, and sometimes succeeded – one thinks of John Hinckley hitting President Reagan in 1981. And Barack Obama was never just another presidential contender; as the first African American to come even close to the highest political office on the planet, in a country whose history is spattered with the blood of racial animus, he is, by common consent, a target several orders of magnitude more tempting than the average for an extremist fringe of kooks, crazies, anti-government militia types, Ku Klux Klan members and other white race warriors, all of whom tend to be unforgiving in their ideological fervour, not to mention armed to the teeth.

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He was granted 24-hour Secret Service protection just a few months into his campaign, in May 2007, after his friend and fellow Illinois senator, Dick Durbin, raised the alarm on his behalf. (Usually candidates receive that protection far later in the election cycle, after they have their party primaries sewn up.) We don't know exactly how hard the Secret Service has had to work on his behalf, although we do know that two men from the old confederate South – one from North Carolina, the other from Florida – were arrested and charged with making threatening statements against him in July. We know that effigies of Obama being lynched, or sliced through the head with a hatchet, have popped up periodically around the country – one on the campus of the University of Kentucky, another in Orange County, California in the run-up to Halloween.

We also know that Obama's supporters have been almost maniacal in their desire to prevent him sharing the tragic fate of the Kennedys and Martin Luther King. On a couple of occasions during primary season, when security ' guards at Obama campaign events stopped searching people's bags because of the backlog of people trying to get in, sympathetic reporters, bloggers and ordinary members of the public complained as loudly as they knew how. Likewise, when someone at a Sarah Palin rally in Clearwater, Florida in early October reacted to a mention of Obama's name by shouting "kill him!", there was such a clamour on the internet that the Secret Service made a rare public announcement saying it was launching an official investigation.

How much of a risk of assassination does Obama face? The most immediate, comfortable answer to that is: not much. The Secret Service has vastly improved its procedures and protocols since the spate of political assassinations of the 1960s and early 1970s. No president would now be allowed to drive at a snail's pace in an open-top car through the centre of a major city, as John Kennedy did in Dallas on 22 November, 1963. The sheer numbers of Secret Service members assigned to presidential protection has increased dramatically since the attempt on Reagan's life – we don't have exact figures on how much, but we do know that when one unhinged man toyed with the idea of tossing a grenade at President Bush in Atlanta in 2005, he never got remotely close enough to give it a real try.

The more worrying answer is that Obama will almost certainly inspire a large number of assassination plots because of the colour of his skin, and that it only takes one of them to be blessed with luck, proper organisation and a little official incompetence to pose a serious threat. When asked how much of a risk he faces, he has acknowledged that the color of his skin will be a problem for some people. And he knows that Colin Powell, the only other African American of significant stature in recent times to consider a run at the White House, decided not to pursue the presidency in part because his wife, Alma, feared for his safety.

"There's not any question he's under more threat than most politicians," said Mark Potok, one of America's leading researchers into hate groups who edits a monthly Intelligence Report for the Alabama-based Southern Poverty Law Center. "I think we are seeing a kind of perfect storm of conditions that might well help white supremacist movements grow, and grow rapidly.

"We have changing demographics, and the Census Bureau projection that whites will lose their majority status in America by 2040. We have the tanking economy, and now... a black man in the White House. This makes some Americans feel they are losing their world – the sense that the country their forefathers built is slipping away from them."

The number of racist hate groups tracked by the Southern Poverty Law Centre has grown by almost 50 per cent during the Bush administration years, from about 600 in 2000 to almost 900 now. In contrast to the 1990s, when the "angry white man" phenomenon fuelled the militia movement and led to the white-supremacist inspired Oklahoma City bombing, much of this new growth has been triggered by virulent hostility to immigrants pouring in from Mexico.

It is entirely possible, though, that the emphasis will change now that Obama is about to enter the White House. Certainly, the neo-Nazi movement senses an opportunity: to judge by the endless chatter on far-right websites, they see a President Obama as the best recruiting tool they've had in years. "Obama will be a signal, a clear signal for millions of our people," the former Louisiana Ku Klux Klan leader and erstwhile candidate for governor, David Duke, wrote earlier this year in an essay he called A Black Flag for White America. "Obama is like that new big dark spot on your arm that finally sends you to the doctor for some real medicine. ... Obama is the pain that let's [sic] your body know that something is dreadfully wrong... Millions of European Americans will inevitably react with new awareness of their heritage and the need for them to defend and advance it."

That logic suggests the far right is not, in fact, itching to pull the trigger on Obama. Except that we are hardly dealing with rational people. The neo-Nazi magazine National Socialist wrote a cover story in September purporting to debunk the "myth" that Obama might be assassinated. But the cover also showed a photograph of the candidate in the crosshairs of a rifle (altered to look like a swastika) under the headline: "Kill this NIGGER?" And the piece went on to suggest that Obama, backed by Communists and Jews, planned to commit genocide against working white people.

Likewise, the "imperial wizard" of the Ku Klux Klan, an Indiana railway worker who calls himself Ray Larsen, denied any intent to attack Obama when interviewed on television a few months ago. But he added: "If that man is elected president, he'll be shot sure as hell."

If that doesn't have the Secret Service worried, it should. Some security experts have already started drafting memos with ideas on how to keep Obama better protected using state-of-the-art technology – for example, hand-held TeraHertz scanners that would-be assassins could not spot. Martin Dudziak, a Virginia-based security specialist who has worked on counter-terrorism issues, pointed out glumly that it is unusually difficult to profile would-be attackers. As he put it in a memo drafted in October: "There are frankly and very unfortunately, a lot of people in the USA who have deep-rooted 'phobic' hatred of an African American... being president. We should not try to deny this sombre reality."

If the inept Denver plot was not warning enough, news of another planned anti-Obama assault broke at the end of last month with the arrest of two White Power advocates in Tennessee. Daniel Cowart and Paul Schlesselman didn't appear to be any more competent than Adolf and Gartrell. They had grand schemes to kill more than 100 African Americans, and fantasised about killing Obama dressed in white dinner jackets and top hats, but they couldn't so much as rob a house – they gave up on their intended target after spotting a guard dog out back and got picked up after shooting out the windows in a church.

Still, they had some serious weapons: a sawn-off shotgun, high-powered rifles and a couple of handguns. And Cowart appears to have been a founding member of a hate group called the Supreme White Alliance. While their dreams of killing Obama might have been fanciful, some of their other plans might not. "They might well have shot up a black high school, or hurt a group of black children," Potok said.

And it is entirely conceivable that other, more competent criminals will follow them. Obama may not have appeared remotely daunted when he delivered his victory speech in Chicago's Grant Park on election night, but it is worth remembering that he was also speaking behind a bulletproof glass shield. Such precautions, one suspects, will be the rule rather than the exception over the next four or eight years.

"There is a boiling rage just beneath the surface," Potok added. "We're talking about a minority, clearly, of whites. It's hard to say how large that group of people is. But I think this represents the beginning of a real white backlash in a certain quarter of the population."