Washington, USA - One presidential hopeful is a preacher, another proudly Mormon, and most openly tout their Christianity. In an arena where faith can make or break a politician, the one in 10 Americans who profess no religion feel left in the cold.
"They're very disconcerted," said Darren Sherkat, an atheist sociology professor specializing in religion at Southern Illinois University.
"They're horrified by both the Democratic and Republican rhetoric surrounding religion -- that people who are not religious ... are immoral, that they're not qualified to serve in public office," he said.
Ian Thomas, 25, got involved in political campaigning as a student and in 2005 ran for a place on the school board in his local district in Pennsylvania.
Days before the vote, a county council member emailed local community groups disparaging Thomas for having an atheist bumper sticker on his car, and for writing a letter about atheism to a local newspaper.
"They are entitled to their beliefs and free speech but it doesn't make a sound foundation for elected officials who makes our laws ... to promote an Atheist that we know anything about," read the ungrammatical email, shown to AFP.
"I was very, very insulted," Thomas said.
The small-town incident was part of a wider pattern of "disenfranchisement" of non-believers, according to Margaret Downey, president of the educational organization Atheist Alliance International.
She claims atheists are "the fastest-growing minority in America."
But they are also "the least tolerated group by conventional standards of religious toleration in the US," Sherkat said.
While church and state are constitutionally separate, politicians must reckon with a largely religious electorate -- some 160 million out of the 200 million adults considered themselves Christian, according to 2001 figures from the US Census Bureau.
Critics complain that candidates face a public "test" of their faith credentials.
"Atheists and agnostics find all the candidates distressingly religious," said Michael Shermer, an atheist writer and publisher of Skeptic magazine.
"Legally, there is no religious test for office, but culturally there obviously is," he said, as polls showed Republican Mike Huckabee, an ordained Baptist minister, surging ahead in key early nominating states.
Religion surfaced prominently when Huckabee's rival Mitt Romney, a member of the Mormon church, made a bid this month to reassure the powerful conservative Christian voting bloc.
"I will take care to separate the affairs of government from any religion, but I will not separate us from the God who gave us liberty," Romney said, fighting to dispel mistrust of his denomination, which some dismiss as a sect.
"Yeah, well, what about the approximately 30 million American nonbelievers, Mitt?" Shermer retorted, in comments to AFP. "You have no plans to represent us, or to protect and defend the constitution for us?"
More than one in 10 US adults have no religious affiliation, according to the census figures. But a Gallup poll in February found more than half of voters would not back an otherwise well-qualified candidate from their favored party if that person was an atheist.
"We're very saddened that people walk into the voting booth and do bring their prejudices, in terms of only voting for people who believe in God," said Lori Lipman Brown, head of the Secular Coalition for America, a Washington-based group campaigning for separation of church and state.
"People have this prejudice against non-theists and think that we don't have values or morals or share their ideas on issues, or live compassionate lives," she said. "All of which is not true. But they're going to vote based on those prejudices."
Non-believers would not necessarily reject a candidate who was religious, according to campaigners.
"Non-theists don't have any problem with people having their religion ... You shouldn't be walking into the booth thinking,'I'm going to vote for or against someone because of what he or she believes,'" says Lipman Brown.
"The fair question would be to ask ... will you impose your theology on civil law?"
"There is no candidate that an atheist would vote for ... other than maybe Ron Paul," Shermer said, naming a Tennessee lawmaker, a long-shot Republican contender.
"He's a libertarian who feels absoutely (for) separation of church and state."
"Many of the candidates would be acceptable to me regardless of their religious faith," Stark told AFP. "Jimmy Carter (who became president in 1977) was perhaps the most personally strident conservative Christian -- and I think he did a wonderful job."