Greene is set to speak at the monthly meeting of the local NAACP branch in his hometown of Manning. It's the first known public speech for Greene, who's spoken only in a series of awkward, terse and confusing media interviews. Interest in Sunday's appearance is so high that the meeting was moved twice - first to a larger church, then to the local junior high school's gymnasium.
"The interest is really starting to swell," said Bobby Fleming, president of the Manning branch of the National Association for the Advancement of Colored People.
Greene won an unexpected victory June 8 over former state lawmaker Vic Rawl to earn the chance to try to take down Republican U.S. Sen. Jim DeMint. Also challenging DeMint is Green Party candidate Tom Clements.
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An unemployed military veteran who lives at home with his ailing father, Greene has called himself "a true American hero" and suggested last week the creation of action figures of his own likeness as a way to create jobs in South Carolina.
Greene said he campaigned in the weeks leading up to the primary, but he has refused to name anywhere he spoke, and no one has come forward to say they saw him try to woo voters outside of his barber shop in Manning.
Greene won't reveal much about what he plans to do with the kickoff to his campaign. "I'll just be talking about jobs, education and justice," said Greene, repeating the only three topics on the "issues" section of his new website.
Fleming has known Greene for most of his life. Their fathers attended American Legion meetings together. Greene's late mother ran a flower shop, and Fleming said he remembers the woman - with young Alvin in tow - often coming to make deliveries at his family's funeral home.
"He was always willing to help his mother out," said Fleming, recalling how Greene was dwarfed by the large arrangements he carried through the halls.
Fleming said the NAACP, which doesn't endorse candidates but tries to educate voters, decided to invite Greene after the State Law Enforcement Division cleared him of any criminal charges on how he got the money to pay his $10,440 filing fee.
Greene still faces a felony charge of showing obscene Internet photos to a University of South Carolina student. He has refused to talk about the case.
Candidates had to report this week how much money they have raised. Greene said he didn't meet the $5,000 threshold that would have required him to file. He said he has raised only about $1,000.
Fleming said the story of how Greene has gone from unknown even in the town of 4,000 where he grew up to a major party candidate in a state of almost 4.6 million people reminds him of the biblical story of David and Goliath.
"David was chosen by God to fight the giant," Fleming said. Greene is "new to politics but he feels this strongly. He wants to make a difference."