U.S. Republican presidential candidate Jon Huntsman withdrew from the race on Monday, endorsing leading candidate Mitt Romney.

"We step down with even greater appreciation of the American democracy, and we respect the results," Huntsman told supporters at a press conference in South Carolina.

"To our many supporters and volunteers, I offer my heartfelt thanks," said the former Utah governor and President Barack Obama's ambassador to China. "Mary Kaye and I are equally humbled and amazed at the outpouring of support we’ve received from friends and complete strangers."

Huntsman’s leaving the race leaves just five men in the race heading into South Carolina's critical Saturday vote. With a victory of presidential candidate Romney likely, his nomination seems inevitable.

Romney stood alone Monday at the top of the field of Republican candidates in this week's primary balloting in South Carolina. Romney previously was first in Iowa caucus voting, then in the New Hampshire primary polling last week.