Controversies surrounded the Democratic nominee, Alvin Greene. Greene's primary election win and his margin of victory surprised pundits. As of the primary, he had held no public campaign events, raised no money, and did not have a campaign website. A review of the primary election showed that of the state's 46 counties, half had a significant gap between the absentee and primary day ballots. For example, in Lancaster County, Vic Rawl won the absentees with 84 percent, while Greene won primary day by a double digit margin. Rawl's campaign manager also claimed that "In only two of 88 precincts, do the number of votes Greene got plus the number we got equal the total cast."
U.S. Congressman James Clyburn recommended Greene drop out of the race or he would face a federal investigation into his candidacy – even as he faces a felony obscenity charge in Richland County from November 2009. Clyburn said "There were some real shenanigans going on in the South Carolina primary. I don't know if he was a Republican plant; he was someone's plant." Political blog FiveThirtyEight's Tom Schaller suggests three possibilities: a legitimate vote, the vote was rigged, or the vote-counting software was corrupted. Schaller ruled out the possibility of Republican infiltration, similar to Rush Limbaugh's "Operation Chaos" in 2008.
Green Party challenger Tom Clements won the endorsement of the Greater Columbia Central Labor Council of the South Carolina AFL-CIO, a coalition of labor unions. Although the national media and Rasmussen Reports typically do not include Clements in their coverage of the race, the Clements campaign has received regional media coverage. The September 7 Columbia City Paper featured Clements on its cover. The paper noted that the Clements campaign was "starting to get some considerable media coverage, both locally and nationally". A Winthrop University poll conducted between October 5 and 10 of 741 likely South Carolina voters found Clements running second with 12.2% of the vote against 11.2% for Democrat Alvin Greene and 58.3% for incumbent Jim DeMint. An October 13 article in the Columbia Free Times noted that prominent Democrats were privately donating money to the Clements campaign. According to the FEC, as of September 30, Clements for Senate had raised $34,334. Jim DeMint had raised in excess of $3 million. Alvin Greene reported no fundraising activities.
Write-in candidates also joined the race, including the Reverend Mazie Ferguson, Mauldin High School teacher Greg Snoad, Michael C Neumann citing the disparity between the direction the government is headed and the will of the people, and chef Nathalie Dupree, who insists that DeMint is spending too much time campaigning in other states, while Greene is failing to challenge DeMint. Mazie Ferguson was endorsed by House Majority Whip Jim Clyburn in late August. Clyburn said he would not vote for his party's nominee due to Alvin Greene's felony indictment.
Jim DeMint largely campaigned outside South Carolina for Republican Senate candidates identified with the Tea Party. Diverse media outlets have frequently referred to DeMint as a party "kingmaker" for supporting successful primary challengers to mainstream Republican candidates.
At an October 3 appearance before a rally at Spartanburg North Baptist Church, DeMint reminded the audience of his 2004 comments that gay men and sexually active single women should be prohibited from teaching in public schools. The Spartanburg Herald-Journal reported:
'DeMint said if someone is openly homosexual, they shouldn't be teaching in the classroom and he holds the same position on an unmarried woman who's sleeping with her boyfriend — she shouldn't be in the classroom. “(When I said those things,) no one came to my defense,” he said. “But everyone would come to me and whisper that I shouldn't back down. They don't want government purging their rights and their freedom to religion.” 
The remarks attracted national media attention, largely critical. DeMint defended the statements, saying that local school boards should decide the issue. Challenger Tom Clements condemned DeMint's stance in a subsequent interview with the Herald-Journal:
“He's trying to push his version of religion onto the entire country. And I believe in separation of church and state. And I do believe that gay people should have equal rights,” Clements said. “That's his belief, but I don't think he can force that on society as a whole or the public school system.”
^Meet The Press. Transcript for October 17, 2004. Guests: Ken Mehlman, Bush-Cheney '04 Campaign Manager, Bob Shrum, Kerry-Edwards '04 Campaign Chief Strategist, Rep. Jim DeMint, (R-S.C.), Republican Senate Candidate, Inez Tenenbaum, South Carolina State Superintendent of Education, Democratic Senate Candidate.