Mike Huckabee has announced that he will not seek his party's US presidential nomination in 2012, adding uncertainty to the race to pick a Republican challenger to President Barack Obama.
"All the factors say 'go', but my heart says 'no' and that's the decision that I have made," he said on his Fox News Channel programme on Saturday night.
"My answer is clear and firm: I will not seek the Republican nomination for president this year," Mr Huckabee added.
A former governor of Arkansas, Mr Huckabee had been riding high in some 2012 polls among Republicans. But he had not been raising funds or touring the country as he wrestled over whether to launch a second run for his party's nomination or stick with his Fox show, Huckabee.
Mr Huckabee, who unsuccessfully sought his party's presidential nomination in 2008, said he had his family's full support, promising poll numbers, and evidence that he could carry states beyond the US South and appeal to voters beyond social conservatives.
But he said private reflection on his decision to stay out of the race gave him a "clarity and an inexplicable inner peace".
Mr Obama was far ahead of all possible Republican candidates mentioned in a Reuters/Ipsos poll this week. A number of high-profile Republicans have either declined to run or are still weighing their options.
The former Massachusetts governor Mitt Romney is expected to run, as is the former Minnesota governor Tim Pawlenty, who analysts say would attract the kind of evangelical, conservative voters who would have backed Mr Huckabee.
Mr Pawlenty said in a statement: "Mike and I agree our nation is facing big challenges and desperately needs new leadership and I plan to work hard to earn the support of the millions of Americans who have supported him."
The former House of Representatives speaker Newt Gingrich became a candidate last week, along with a number of long-shots, including the libertarian-minded Texas Representative Ron Paul. Still on the fence are the Indiana Governor Mitch Daniels, the former Alaska governor and vice-presidential candidate Sarah Palin and the Minnesota Representative Michele Bachmann.
Mr Obama, who made history in 2008 by becoming the first African-American president, leads possible Republican candidates by double digits.
The president's approval rating is at 49 per cent, a 3-point increase over last month, amounting to only a modest bounce after the May 2 killing of the al- Qa'ida leader Osama bin Laden. Other surveys have given Mr Obama a slightly larger post-Bin Laden boost.