Former Utah governor Jon Huntsman has decided to end his presidential candidacy and will formally exit the race on Monday, according to two sources briefed on his thinking. He is expected to endorse former Massachusetts governor Mitt Romney.

“This was his decision alone,” said one former adviser. “Alone.”

View Photo Gallery: The former U.S. ambassador to China and governor of Utah will formally end his presidential candidacy Monday.

Huntsman had pledged to soldier on after a disappointing third place finish last week in New Hampshire’s primary. He insisted his showing amounted to a “ticket to ride” to South Carolina.

But, political reality seems to have hit Huntsman and his team over the last few days as polling in the Palmetto State, which will hold its primary on Jan. 21, showed him in single digits.

"There was no sense standing in the way of Romney,” said one Huntsman adviser. "Every vote we took in South Carolina and Florida was from him."

Huntsman’s decision comes less than 24 hours before the six remaining candidates were scheduled to take the stage in Myrtle Beach for a debate. It was one of two debates set for the week, a prospect Huntsman didn’t relish.

Huntsman’s campaign, which was built by a team of advisers while he was still in China serving as the U.S. Ambassador to that country, never seemed to gain the necessary altitude to boost him into the top tier.

He was, from the start, a media darling — profiled in a variety of national magazines and newspapers. His daughters — the three oldest — became a social media phenomenon known as the “Jon2012” girls.

And yet, for all of the buzz surrounding Huntsman, he never seemed able to put it all together. While his campaign aides insisted the Republican electorate was ready for a common sense conservative, Huntsman’s moderation — in tone if not in all of his policies — left him as a man without an obvious constituency within the Republican party.

His early performances on the campaign trail and in debates didn’t help matters. He was wooden and lacking in charisma; his reference to a Nirvana song during one early debate left the political world scratching its collective head about just who he was appealing to.

Huntsman also struggled to raise money although a super PAC with his father’s financial backing did spend heavily on his behalf in New Hampshire.

But, after deciding to skip Iowa’s caucuses, the New Hampshire primary turned into an all or nothing gamble for him. Huntsman lavished attention on the state and gained some momentum in the closing days before the Granite State vote but still finished well behind Romney and Texas Rep. Ron Paul.

His decision to quit the race and throw his support behind Romney should help the former Massachusetts governor in South Carolina as he is now the lone candidate in the field making a direct appeal to the establishment wing of the GOP.

Polling suggest Romney, who has already won the Iowa caucuses and New Hampshire primary, is the frontrunner in South Carolina although former House Speaker Newt Gingrich and former Pennsylvania senator Rick Santorum are also heavily targeting the state.

Huntsman is the second candidate to quit the race since voting began in Iowa on Jan. 3. Minnesota Rep. Michele Bachmann stepped aside after a disappointing finish in Iowa.