Is Alvin Greene the least likely US senator in history?

He did not campaign, yet won the Democratic primary for South Carolina by a mile. How? David Usborne reports from Manning

No candidate for the US Senate could hope for a kinder setting for the kick-off event of his campaign. There are pastors and preachers, a rousing church choir, two soloists, a full house of supporters jostling to see him up close and an invasion of TV cameras the likes of which this tiny town has never seen. Yet, seated on the stage in the gym of Manning Junior High, the man of the hour, Alvin Greene, 32, looks more terrified than thrilled.

The build-up to his taking the microphone lasts an hour and while the mostly African-American audience vibrates with anticipation and sways to the bursts of music, he is immobile but for the occasional dabbing of sweat from his brow and fiddling with his notepad.

Plenty of stars should be aligned for Greene as he prepares to do battle with the incumbent Jim DeMint, a conservative Republican, ahead of elections in November. He is the first black candidate for the US Senate from South Carolina since the Reconstruction Era from a county that played a pivotal part in the first stirrings of the Civil Rights struggle. He is young, served in the military and is fresh to voters. Moreover, on the curiosity scale of political science, Greene is off the charts. Here, however, is where the story of his run for high national office takes a trickier turn. It could conceivably be fairy tale, but increasingly risks veering towards freak show. Alvin Greene is the candidate that shouldn't be, unless every political observer is missing something. No one knows how it happened, and no one knows how it's going to end.

This is not just the first campaign event held by Greene since he defeated his Democrat rival, former Charleston judge and state lawmaker Vic Rawl, in the primary election in June making him the party's chosen candidate to take on DeMint. It is his first ever. In other words, he won the primary without campaigning. (He did spend $1,000 (£650) on some leaflets.) He had no staff, no battle bus, nothing.

Worse, he still doesn't. Greene is an unemployed veteran, who was discharged involuntarily (though not dishonourably) from the US army nine months ago. He receives unemployment benefits, does not own a computer, lives with an ageing father in a modest home a few miles from here and, so far as anyone can see, still does not have any kind of campaign staff. As he is hurried off the stage at the end of the afternoon's proceedings, members of the media look for his spokesman. There is no such person.

Some are in this room because they feel that since his election – he stomped over Rawl, taking 59 per cent of the vote – Greene has been victimised, even by the Democratic Party which reacted first by asking him to step aside to allow a more established figure to run. (He demurred.) "We cannot allow people to vilify young people just because they win an election," railed Willie Bethune, a local black leader who introduces him to the crowd. "Politics is about how many votes you get in the box and he had a whole lot."

Greene exposed himself to a limited number of interviews after his win and the results have not always been pretty. "He speaks in an uninflected monotone, repeatedly trails off mid-sentence and often mumbles incoherently," offer Newsweek in its latest issue. There was widespread mirth when he told one interviewer that his state's economy might benefit from a new cottage industry making Alvin Greene action figures. That led a minor league baseball team owned by the actor Bill Murray in Charleston to begin selling tiny Statue of Liberty dolls to its fans doctored to show the facial likeness of Greene.

To be genuinely puzzled is surely fair, however. How is it possible in this land of dollar-greased democracy, that someone like Greene could not only triumph in a US Senate primary by so wide a margin without campaigning? Jim Clyburn, a prominent US Congressman from the state, had his theory: "I don't know if he was a Republican plant," he said in the immediate aftermath of the vote. "He was someone's plant."

This would imply that the watching media hordes – especially the particular crowd that has chosen to spend a Sunday afternoon in his company here in Manning – are all victims of some kind of elaborate electoral fraud. An April fool that was sprung in June and won't fulfil its course until election day in November.

The mortification and bafflement of the party and many Democrat voters here remains profound. "We are looking for a little enlightenment like the rest of you are," notes Rick Norred, the school's assistant head, who has his own theory of how Greene won in June. "I think people are willing to vote for the people they don't know because they are disgusted with the people they do know." If this is to be the year of an anti-incumbency movement, then Greene should be its poster boy.

More distressed is Matey Ward, a 68-year-old retired history teacher who has come from Charleston to hear Greene speak. "I just really hope that there's some 'there' there," she says, tapping her head to indicate the hoped-for repository of the candidate's intellect. "Right now I feel disenfranchised. I am still reserving judgement but from what I've heard so far I just don't see who I am going to vote for. I would poke pins in my eyes before voting ever for DeMint."

Part of what occurred, perhaps, was a failure by journalists to examine Greene's record ahead of the primary polling. If they had, they would have asked precisely why he was discharged from the armed forces after 13 years of service (including a brief tour in England) and what prompted the army to demote his rank while he was in South Korea from 2007 to 2008. They would surely also have found that Greene was – still is – facing trial on state obscenity charges of showing pornographic material to a female university student. But none of this happened, and so Candidate Greene he is.

When he finally takes the microphone, Greene offers a speech that mostly recycles the few, barely radical, policy ideas he has previously raised in his media interviews (though not the action doll idea). They include his call, repeated three times, for getting "South Carolina and America back to work for the people again". There is also the immortal, and more or less irrefutable, statement: "Instead of doing less for education, we ought to be doing more". Eager for him to shine, the crowd applauds often. The enthusiasm seems almost to confuse Greene, whose darting eyes betray alarmed pleasure.

Then he gets to another favourite theme – how the justice system is too quick to put offenders on trial and thereafter in prison – and nearly loses his own plot. There is "this guy" a "person of colour", he begins, who has been in legal trouble recently and... Suddenly he seems to change his mind about going further with the story – possibly, you feel, because it may not reflect especially well on its teller – and drifts into a mumble. "But anyway, moving on...."

State prosecutors have postponed Greene's obscenity trial – he was charged last November – removing what could have been a grave distraction for his campaign. He also has a lucky escape when the State Law Enforcement Division cleared him this month of financial wrongdoing in connection with the $10,440 he had to fork over simply to file his candidacy for the senate seat. Questions of malfeasance were raised because last November, when the obscenity charges surfaced, Greene signed an affidavit of indigency qualifying him for a public defender. But investigators found nothing to disprove his claim that he had taken the money from savings accumulated from military pay.

It is a difficult dilemma for the state Democratic Party which worries not only that the Greene candidacy will give DeMint, the darling of the Tea Party movement in the Senate, a free pass to continue his conservative reign from South Carolina for another six years, but also undermine the chances of all the other candidates on the party line in November, including those for state governor and for seats in the US House of Representatives. "The politically expedient thing would be to distance ourselves [from Greene]," Bakari Sellers, a Democrat State legislator, recently posited. "But we're dealing with a human being. We don't want to end up with an individual that's scarred for life."

All of which leaves Greene to declare full steam ahead with his campaign. "I'm the best candidate in the United States Senate race here in South Carolina," he boldly asserts on stage. Never mind that his campaign headquarters is his dad's home, that he has $1,000 available for his campaign against the $3.5m stashed in DeMint's campaign coffers, or that his own party seems unwilling to give him any help even if there has been some word of loaning him a political handler or two.

We could not get to the end of the proceedings without someone evoking David versus Goliath. Just the slimmest prospect of him toppling DeMint will guarantee that this race will be watched as closely as any other in the land. And if not a political miracle, there will instead be a human tragedy to witness.

Judging by his performance at the school here, Greene is doomed to the latter. Or so says Ms Ward, whose mind, she insists, had still been open on her arrival. "Pitiful, really, wasn't it?"