— On Monday, Mitt Romney finally got the Jon Huntsman endorsement he thought he’d been promised long ago.

Six years ago, after a private dinner with their wives, Romney came away believing he would have Huntsman’s backing for president, according to a Romney adviser. Romney was so sure of the then-Utah governor’s support that he asked him to write position papers on China, a country Huntsman knows well. Romney even shared internal strategy with him.

Then, in July 2006, Romney found out from news reports that Huntsman had officially endorsed Sen. John McCain (Ariz.). A source close to the Huntsman family countered said that any depiction of Huntsman misleading Romney was “fabricated.” Nevertheless, Romney saw the endorsement as a stinging, personal rebuke — one that further alienated the governors, who did not know each other well but whose families did.

For years, the scions of two of the country’s most prominent Mormon families — they are, in fact, distant cousins — had waged an uneasy and at times bitter rivalry that would only intensify once the prize became the White House.

Huntsman’s awkward embrace of Romney on Monday underscored the strained relationship between the two men.

With his wife, Mary Kaye, and four of their usually ebullient daughters looking on stoically, Huntsman announced the suspension of his campaign in a drab conference room here. Romney did not appear at his side, nor did the two men make plans to campaign together before Saturday’s South Carolina primary.

Shortly after the news of Huntsman’s withdrawal broke Sunday night, Huntsman called Romney. The two men spoke briefly and Huntsman agreed to record a phone message for Romney, according to a Huntsman aide.

In a nearly nine-minute speech here, Huntsman mentioned Romney just once, leaving little doubt that his endorsement was primarily in the name of party unity.

“I believe it is now time for our party to unite around the candidate best equipped to defeat Barack Obama,” Huntsman said. “Despite our differences and the space between us on some of the issues, I believe that candidate is Governor Mitt Romney.”

With his father, Jon Huntsman Sr., watching from the wings, Huntsman sternly called on the other candidates to cease the “onslaught of negative and personal attacks not worthy of the American people.”

Reporters preferred to revisit Huntsman’s attacks on Romney. As he left the stage, they shouted questions about him having called Romney “completely out of touch” and “unelectable because he lacks a core.”

Huntsman simply walked out the door. By early afternoon, an aide said, he was on an airplane with his family — trying, for a moment at least, to forget about his failed campaign.

Driven and gifted

Huntsman and Romney are both driven and gifted men with deep roots in their church’s moneyed establishment. Huntsman is a son of one of America’s most successful Mormon industrialists; Romney, of one of its most prominent politicians.

Their families are intertwined. Huntsman’s mother, Karen, roomed with Romney’s sister Jane at the University of Utah. Karen’s brother, Bruce, dated Romney’s older sister, Lynn. And Karen’s father, David Haight, a church apostle, was a childhood best friend of Romney’s father, George.

The ambitions of Romney, 64, and Huntsman, 51, first collided in 1999, when the scandal-plagued Olympic Winter Games in Salt Lake City sought a new leader. Both men pursued the job aggressively, seeing it as a springboard to a political career. After much behind-the-scenes politicking, Romney won the job.

It was a stinging defeat for the Huntsmans, considering how hard the family patriarch, Jon Sr., had lobbied for his son.

“It was a painful, miserable loss for the Huntsman family,” said one family confidant, who spoke on the condition of anonymity. “Two powerful juggernauts competed over the most important thing in the home state of their religion. One won and one lost. And one not only won the prize, but elevated himself on a national platform by running a successful Olympics.”

In the 2008 campaign, the elder Huntsman dutifully raised money for Romney. His son’s decision to side with McCain prompted angry phone calls from Romney, Karen Huntsman said in an interview last year.

By the spring of 2011, as Romney launched his second presidential bid, Huntsman’s supporters were laying the groundwork for his own campaign.

After Huntsman returned from China, where he had been President Obama’s ambassador, he discovered that money and support from his home state — where he had been reelected governor in 2008 with 78 percent of the vote — were going Romney’s way.

Utah’s senior senator, Orrin G. Hatch, and nearly 70 other state elected officials backed Romney. So did Rep. Jason Chaffetz, who had been Huntsman’s chief of staff. And in what many Utah Republicans interpreted as a rejection of Huntsman, Sen. Mike Lee, who was his counsel as governor, stayed neutral.

Gov. Gary R. Herbert, Huntsman’s running mate and successor, was prepared to endorse Romney until Huntsman’s father talked him into staying on the sidelines, according to a Republican with knowledge of the talks who spoke on the condition of anonymity.

“People struggled with who to support because supporting one doesn’t necessarily mean you don’t like the other,” said Thomas Wright, the state Republican Party chairman, who was unaligned but said he is now backing Romney.

Lew Cramer, Huntsman’s appointee to run the Utah World Trade Center, was a key fundraiser in 2008 for Romney, a college classmate. But with Huntsman entering the race, he was torn.

“They’re both very talented, smart and great thinkers with a beautiful head of hair,” said Cra­mer, who signed on as a Huntsman fundraiser. “I certainly got a lot of abuse from my friends on the Romney campaign, saying, ‘You’re a rat.’ . . . Let’s face it, Mitt had all the help he needed, but Jon, his loyal friends had to rally around him.”

‘In the hunt’ and out

In the race, Huntsman and Romney fought over the same voters — two moderates in a field full of conservatives. Firmly positioned at or near the top of the polls all year, Romney largely ignored Huntsman. Stuck at the bottom, Huntsman occasionally went after Romney.

This month, he said of Romney that Americans would have trouble finding “a gut-level trust when it comes to someone who has been on so many sides of major issues.”

Huntsman’s relatives and advisers had been even more cutting.

His father lashed out at Romney’s ideological inconsistency, telling the New York Times last fall: “I’ve worked for three different Romneys. . . . If you need to win that badly, I guess you just kind of do what you have to do to get a vote.”

Huntsman’s daughter, Liddy, 23, said she would “absolutely not” vote for Romney. “I just don’t trust him. I don’t trust his record. I don’t trust his character,” she told the Daily Beast last fall.

This past week, even as his candidacy collapsed, Huntsman took to saying he was still “in the hunt.”

But except for some rare flashes, Huntsman failed to demonstrate the killer instincts required to remove Romney from his political path.

“He was a shooter, a target shooter, but he was not a killer,” Huntsman’s younger brother, Peter, said in an interview last year.

He recalled that as children, the two boys would shoot their rifles behind the family estate outside Salt Lake City. “I hunted deer and would shoot rabbits.”

“And Jonny?” interrupted their mother, Karen.

“No,” Peter clarified. “He was more at peace with the rest of society.”