Mitt Romney
Mitt Romney gets credit for perhaps the most overused stump-speech line in the 2012 campaign.

Why have Republican supporters been so hesitant in voting for the former governor of Massachusetts becoming the presidential candidate for the party?

Mitt Romney should have tied up the nomination before the primaries began on 3 January but has struggled to steam ahead of rival candidates who have flooded the airwaves with attack ads.

National editor of the online political publication, Politico, Charles Mahtesian, told International Business Times UK: "On paper he is the perfect candidate. He has been successful in business, he has served as a serviceman and has worked in public office as governor.

"The problem is authenticity, which he doesn't have and is the most important things in American politics. He is almost too squeaky clean and this has caused some to be concerned over whether he is genuine or not."

The attack ads from rival candidates have attempted to dislodge Romney from his strong poll lead.

The latest assault came from Newt Gingrich, the former speaker of the House of Representatives, who said Romney had engaged in exploitive capitalism as a businessman.

"If Romney wins, conventional wisdom holds he will have the nomination locked up if he continues that winning streak in South Carolina, the first Southern state to vote," said Mahtesian. That would make him the party's standard-bearer against President Barack Obama in the November election. South Carolina Republicans will vote for their presidential candidate on 21 January.

Romney says his business experience makes him better prepared than Obama to rebuild the wobbly US economy. The slow recovery from recession has left Obama vulnerable as he runs for a second White House term.

After resisting calls to open his tax records for public scrutiny - a tradition for presidential candidates in recent decades - Romney said he would consider making his returns public in April. April is the month when Americans must file income tax returns with the federal government. Many candidates in the past have baulked at demands for public scrutiny but always ended up releasing their returns.

He said the returns would show he paid about 15 percent of his income to the federal government - about 20 percent less than the top rate assessed on the highest earners in the United States.

Romney is sensitive about his money as increasing numbers of Americans are angry about the extraordinary growth in the percentage of the country's wealth that is in the hands of the few.