MYRTLE BEACH, S.C. (AP) — Jon Huntsman abandoned his once-promising campaign for the Republican presidential nomination on Monday and endorsed Mitt Romney as the man “best equipped to defeat Barack Obama.”

The former Utah governor coupled his announcement with an appeal to the remaining contenders to stop attacking one another in television commercials. “At its core, the Republican Party is a party of ideas, but the current toxic form of our political discourse does not help our cause,” he said.

He noted that he and Romney have had differences, and he did not respond when asked if he still believes — as he said while campaigning for last week’s New Hampshire primary — that the former Massachusetts governor is out of touch and unelectable.

Huntsman said he was suspending his candidacy, but his endorsement made it clear that was a euphemism. He dropped out less than a week after finishing third in New Hampshire, where he had staked his candidacy. While he has campaigned in South Carolina for nearly a week, he lacked the money to pay for TV commercials or other essentials of a modern campaign.

Given Huntsman’s decision to back Romney, his departure seemed unlikely to clarify the overriding question of the Republican campaign, whether conservative voters could or would unify behind Rick Santorum, Newt Gingrich or Rick Perry to create a strong conservative challenger to Romney.

Huntsman’s resume had suggested he could be a major contender for the Republican presidential nomination: businessman, diplomat, governor, veteran of four presidential administrations, an expert on China and foreign trade. But the former ambassador to China in the Obama administration found a poor reception for his brand of moderate civility that he had hoped would draw support from independents, as well as party moderates.

Huntsman, 51, was almost invisible in a race often dominated by Romney, a fellow Mormon. One reason was timing. Romney and other declared or expected-to-declare candidates drew media attention and wooed voters, Huntsman was half a world away serving as ambassador to China until he resigned in late April.