Mitt Romney, the long-running but still-vulnerable favourite to win the Republican presidential nomination, is once more facing awkward questions about his personal finances after announcing that he will refuse to share his tax returns with the US electorate.
The decision, revealed during a recent interview, threatens to put the front-running candidate, who is one of the wealthiest men ever to run for the White House, on the back foot heading into the start of the 2012 primary season, which begins with this weekend's Iowa Caucuses.
Almost every would-be President since the 1970s has published their tax return, but Romney announced that he intended to forego that opportunity during an interview with Chuck Todd of MSNBC. He did not seek to justify the decision, but said merely: "I don't intend to release the tax returns. I don't."
The comments were edited out of the interview before broadcast last week, but emerged during extended footage aired at the weekend. Asked about the issue on the campaign trail, Romney added: "We follow the tax laws, and if there's an opportunity to save taxes, we, like everybody else in this country, will follow that opportunity."
The remarks were seized upon by both Democrats and Romney's rivals for the GOP ticket, who have all promised to release their tax returns. "Why does Governor Romney feel like he can play by a different set of rules?" said the Obama campaign. "What is it that he doesn't want the American people to see?"
One possible answer is the size of Romney's bank balance. With a personal fortune estimated at $250m [£160m], critics have long said that he is out of touch with ordinary Americans. In a recent GOP debate, he casually offered to bet Rick Perry $10,000 over a disputed point of fact.
Another answer is Romney's use of tax loopholes. Though he publicly calls for fiscal discipline, it's probable that, like most of America's so-called "1 per cent," he exploits the nation's elaborate tax code to ensure that he pays a far smaller proportion of income to the IRS than the middle-classes. Analysis by the New York Times last week suggested that his burden was around 15 per cent, thanks to a Bush-era concession aimed at hedge fund managers.
A third potential reason Romney wants to keep his tax return under wraps is that it would reveal exactly how much he does, or does not, donate to charities. It would also lay bare the "tithes" he pays to the Mormon Church, in which he is a former Bishop.
Unease over Romney's wealth has been recently aired in GOP debates. He made his fortune at Bain Capital, a private equity firm which rival Newt Gingrich claimed made hundreds of millions of dollars from "bankrupting companies and laying off employees".
The decision not to publish a tax return also opens him to allegations of shameless hypocrisy. During the 1990s, when he tried, and failed, to secure a Senate seat in Massachusetts, Romney repeatedly challenged the incumbent, Edward Kennedy, to release his tax returns to prove he "had nothing to hide".