Former Ambassador to China Jon Huntsman, a likely candidate for the 2012 Republican presidential nomination, sought to explain his time working in the Obama administration in his first major speech since resigning last weekend.

Huntsman, whom President Obama picked as his top diplomat in China, only touched on what could be his biggest political liability in seeking the Republican nomination.

"Give back. As much as you’re able. Work to keep America great. Serve her, if asked," Huntsman told graduates of the University of South Carolina, where he delivered the commencement address. "I was, by a president of a different political party. But in the end, while we might not all be of one party, we are all part of one nation."

Huntsman's speech is his first major public appearance since his resignation, which he offered earlier this year and became effective last Saturday. In the week since, the former Utah governor has quickly laid the groundwork for his potential presidential campaign. He's met with key lawmakers in Washington and set up a federal political action committee. 

His visit to South Carolina is significant because of that state's status as an early destination in the GOP primary cycle.

But the Republican's work for a Democratic president is still seen as a big obstacle to winning the nomination, though GOP lawmakers this week said they didn't view Huntsman's time in the Obama administration as a non-starter with voters.

Huntsman has set no timetable for deciding whether to run, but in Saturday's speech he called for "new thinking."

"Our system needs new thinking, he said. "We need a fresh generation of innovators, leaders, risk takers, entrepreneurs, scientists and activists -- that's you!"

Huntsman sought to draw on his experience as an ambassador to make an optimistic pitch for America.

"I know there are many in China who think their time has come, that America's best days are over. And, there are probably some in this country who have lost confidence and think that China is the next big thing. But these people aren't seeing things from my earlier vantage point of 10,000 miles away," Huntsman said. "The way I saw it from overseas, America's passion remains as strong today as ever."