He also trailed in the polls in South Carolina, a state seldom friendly to candidates who stray from strict conservative values. Religion, too, is a factor, with evangelical voters rejecting Mormons as fellow Christians.
From the start, Huntsman's campaign struggled to gain support. He didn't get into the race until last June, shortly after stepping down as ambassador to China, a post he resigned as governor to take in 2009.
His campaign was widely viewed as having a better chance in 2016, because the 51-year-old didn't have the time to become well known nationally and was far behind other contenders in both organization and fundraising.
Huntsman chose to skip the first test of presidential candidates, the Iowa caucuses, and finished behind Romney and Texas Rep. Ron Paul in New Hampshire, despite last-minute momentum that had him hoping for second place.
Many believed he would not continue his campaign, but Huntsman headed to South Carolina, telling supporting his finish in New Hampshire was a "ticket to ride."
"I'm surprised but not shocked," said Utah advertising executive Tom Love, a longtime friend of Huntsman's. "It's got to be financial."
Love said Huntsman displayed "class" for his willingness to endorse Romney.
"For him to say it's not there, and I'm done and I'll support Mitt, given the bitterness between the two campaigns for so long, I have to take my hat off to him," Love said.
Huntsman routinely cited his accomplishments as Utah's governor on the campaign trail, especially his effort to move the state toward a single, flat income tax rate. He also continued to support civil unions for gay couples and the need to address climate change, despite the unpopularity of those positions with conservatives.
His departure leaves five candidates in the running for the GOP nomination — Romney, Paul, former Pennsylvania Sen. Rick Santorum, Texas Gov. Rick Perry and former U.S. House Speaker Newt Gingrich.
Romney continues to be the front-runner in the race, but his campaign had no comment on Huntsman's leaving the race. Gingrich issued a statement, "with Gov. Huntsman dropping out, we are one step closer to a bold Reagan conservative winning the GOP nomination."
Lew Cramer, head of the Utah World Trade Center and another longtime friend of Huntsman's, said his dropping out of the race "absolutely" makes it easier on Utahns who were torn between backing Romney and Huntsman.
Cramer, who'd supported Huntsman but had sons campaigning for Romney, said he'd already been contacted by friends in the Romney camp Sunday night. "I just have to write some more checks," he said.
Romney, who calls Massachusetts home and served as that state's governor, is seen as a "favorite son" candidate in Utah. In 2008, he won an unprecedented 90 percent of the vote in the Utah GOP presidential primary over the party's eventual nominee, Arizona Sen. John McCain.
Huntsman trailed Romney repeatedly in polls of likely 2012 Utah Republican primary voters. Cramer said it was a "smart move" for Huntsman to endorse Romney. "I hope this is enough to put Mitt over the top," he said.
Cramer said he expects Huntsman to hit the campaign trail for Romney, "if he's asked."
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