MYRTLE BEACH, S.C. — On Monday, Mitt Romney finally got the Jon Huntsman endorsement he thought he’d long ago been promised. Six years ago, at a private dinner with their wives, Romney came away believing he would have Huntsman’s backing for president, according to a Romney adviser. Romney was so sure of the then-Utah governor’s support that he asked him to write position papers on China, a country Huntsman knows well.