Jon Huntsman is to end his campaign to win the Republican presidential nomination, US press reports say.
He finished third in last week’s New Hampshire primary and had been struggling ahead of this week’s South Carolina primary.
Mr Huntsman had hoped for an upset in New Hampshire but polled only 16.9%.
He will announce his withdrawal later on Monday and endorse front-runner Mitt Romney, said campaign officials quoted by AP.
Primaries and caucuses will be held in every US state over the next few months to vote on a Republican candidate before the eventual winner is crowned at the party convention in August.
Low ratings
Mr Huntsman, 51, is a former governor of Utah and served as President Barack Obama’s first ambassador to China.
A fluent Chinese speaker, in the early 1990s he became the youngest head of a US diplomatic mission for a century when he was appointed ambassador in Singapore.
But his campaign for the Republican nomination failed to gain momentum, hardly registering in national opinions polls with only 1% or 2%.
His withdrawal comes after he gained the endorsement of South Carolina’s largest newspaper The State, which said that he and Mr Romney were the “two sensible, experienced grown-ups in the race”, but that Mr Huntsman was “more principled” and offered “a significantly more important message”.
TV debates
Mr Romney won nearly 40% of the New Hampshire vote last Tuesday, but faces a stern test in South Carolina this week.
The staunchly Republican state has a history of backing the eventual nominee in its primary.
Mr Huntsman’s exit will leave Ron Paul, Rick Santorum and Newt Gingrich as the three main candidates chasing Mr Romney’s lead.
After his handsome win in New Hampshire, Mr Romney is more vulnerable in socially moderate South Carolina, and his Mormon faith may be a disadvantage among the many evangelical and other conservative Christians in the state.
Televised debates will be held on Monday and Thursday, before the primary vote on Saturday.
