Jon Huntsman is bowing to the inevitable and quitting the Republican race after trailing in the polls in South Carolina. He will endorse frontrunner Mitt Romney.

This narrows the field to just five: Romney, the former House Speaker Newt Gingrich, Texas Congressman Ron Paul, former senator Rick Santorum, and Texas governor Rick Perry.

The former Utah governor positioned himself to the left of Romney (a fellow Mormon), but his moderate brand of conservatism failed to resonate with a Republican party that has increasingly moved to the right.

His exit from the race comes as no surprise. He opted out of competing in Iowa earlier this month, as he believed the state was too conservative for him to win. Instead, he concentrated his efforts on New Hampshire, where he needed a second place finish. He came third, and surprised commentators when he vowed to fight on, saying third place was "a ticket to ride". But since arriving in deeply conservative South Carolina, he has struggled to gain traction.

Huntsman's personal fortune is estimated at $50m. His father, worth an estimated at $900m, set up a super PAC which advertised on his behalf, but had become wary of throwing more money at the bid. He is not the only family member to take an interest in the campaign; Huntsman's daughters hit the spoitlight when they filmed videos to support their father's flagging campaign, including this spoof of Herman Cain's campaign ad:

The endorsement of Romney will not make a huge difference since Huntsman's supporters are limited in number -- he was polling at around 5 per cent in South Carolina -- but those who did back him will naturally gravitate towards the former Massachusetts governor, a fellow moderate.

Formerly an ambassador to China, Huntsman's sober, diplomatic style in debates meant he failed to capture the imagination of Republican voters, who are keen for charisma and fighting talk.

His departure follows that of former Minnesota governor Tim Pawlenty in August, pizza mogul Herman Cain in December, and Michele Bachmann after the Iowa caucuses earlier this month. Perry, whose polling in South Carolina is barely better than Huntsman's, looks set to be the next scalp.