Mr. Huntsman’s decision prompted a mix of suspicion and resignation among the president’s advisers: suspicion that Mr. Huntsman had not always been straight about his national aspirations, and resignation that, as one presidential strategist put it, “There’s no loyalty in politics,” especially when it comes to across-the-aisle alliances.

Mr. Huntsman, 51, who resigned as ambassador in late April and declined to comment for this article, is joining the presidential campaign scene as a relative unknown outside Utah. Yet he is among those who are being taken most seriously by Mr. Obama’s aides, who after working with him for more than two years say he could be formidable if — and they consider this a big “if” — he can navigate a nominating contest likely to be decided by voters who may view him as too moderate.

He is a Mormon whose missionary work took him to Taiwan, where he became fluent in Mandarin Chinese. He has benefited from the wealth generated by a family business, the Huntsman Corporation, that is one of the largest chemical companies in the world. He opposes abortion rights and supports same-sex civil unions.

But it is his path from the Utah governor’s mansion to the United States Embassy in Beijing and now to the presidential campaign trail that has gotten him particular attention, representing a rare moment in American history in which a member of a presidential administration turns to run against it.

Mr. Obama’s decision to name Mr. Huntsman his ambassador to China in 2009 was hailed by members of both parties as another act of political wizardry, a chance to show that the president was trying to infuse his administration with a bipartisan spirit.