In a foretaste of things to come, a leading Republican said yesterday that the Illinois senator's colour would be worth up to 15 percentage points for his Republican opponent John McCain in November's election, while it emerged that a Pentecostal minister had posted a sign outside his church reading: "Obama, Osama - humm, are they brothers".
Obama is a practising Christian
Pastor Roger Byrd claimed he just wanted to pose questions to his congregation at the Jonesville Church of God in South Carolina.
"It's simply to cause people to realise and to see what possibly could happen if we were to get someone in there that does not believe in Jesus
Christ," he said.
Asked if he believed Mr Obama was a Muslim, Mr Byrd told a local television station: "I don't know. He says he's not. I hope he's not. But I
don't know."
Mr Obama, whose father was a non-practising Muslim from Kenya, is a Christian who regularly worships at the Trinity United Church of Christ in his hometown
Chicago.
Despite repeatedly stating his faith on the campaign trail in a bid to quash rumours that he follows Islam, 15 per cent of respondents in a
recent AP-Yahoo poll thought Mr Obama was a Muslim.
In the same poll, eight per cent of white people said they would be "uncomfortable" voting for a black president.
Although whites have voted for the Illinois senator in large numbers, making him the frontrunner in his nomination battle with Hillary Clinton, he has fared less well among white, working class voters.
In Ohio on Mar 4, Mrs Clinton beat him by 66-33 points among that demographic group, while in Mississippi, one of the poorest states, Mr Obama won 26 percent of the white vote, compared with 70 per cent who backed his opponent.
In recent primaries, black voters have supported him at a rate of nine to one.
Anecdotal evidence from Pennsylvania, which was expected to hand Mrs Clinton a narrow victory, suggests similar racial divisions would play out there.In Clairton, the sort of struggling steel town which has been relatively resistant to Mr Obama's message of unity and hope, some white residents were last week candid about their hostility.
Unemployment has helped foster simmering racial tensions, with blacks blamed by whites for drug dealing and a rise in crime.
Recalling the civil rights era, Jim Alfonsi, a self-employed decorator, said: "Obama has good ideas but the only thing I am afraid of is that if he becomes president we will see the scenes of the 60s again. They might think it's their chance to rise."
Tina Jones, a waitress, confessed that some of her friends "wouldn't vote for him because he's black", adding: "But I don't listen to that, I want to know what they [candidates] are going to do."
Evidence of increasing racial polarisation among Democrat voters has led some Republican strategists to conclude that Mr Obama's mixed race - his mother was a white from Kansas - could hand the party an advantage in swing states such as Ohio and Pennsylvania, with their sizeable working class populations.
A senior member of the party, asking to remain anonymous, told Politico.com: "McCain runs against Barack Obama and the race vote is worth maybe 15 percent to McCain."
The Republican nominee has been adamant that he would not run a divisive campaign, and is spending much of this week reaching out to black voters.
But if Mr Obama becomes his opponent, then secretive Republican interest groups over which he has little control would be certain to exploit the dual targets of the Democrat's race and exotic background, not to mention the similarity in his name with the world's leading terrorist.
Wary of fanning flames, the American media has been reluctant to discuss the glaring divide in racial support for the candidates.
"You could say it's squeamish or handling data responsibly," said EJ Dionne, a leading liberal columnist, adding that high turnouts by African American and young voters for Mr Obama could well offset negative votes.
"This is something that will be talked about during the campaign, but it is very hard to tell how big a factor it will be.
"Electoral races are decided at the margins and how many who wouldn't vote for him because of race wouldn't vote Democrat any way?
"I don't think we yet know the answer to the question. But the answer is clearly not zero."
