IN FEBRUARY, Donald Trump said he hoped to release his tax returns in “three [or] four months.” Progress has not been forthcoming. His excuse for the continued delay is that the taxman is auditing the returns, and that his lawyers say he should keep his papers private in the meantime. If Mr Trump does not release any tax returns before November, he will be the first major candidate since 1976 not to do so. There is no legal reason Mr Trump cannot release his returns while they are under audit. Paul Krugman, a New York Times columnist and economist, has argued that the audit should in fact make him more willing to go public—were no audit underway, he might fear that newspaper headlines would trigger one. A generous explanation for Mr Trump’s stance is that his lawyers think that a crowdsourced effort to find problems with Mr Trump’s (no doubt complex) tax affairs might be more effective—or less forgiving—than that of the chronically-underfunded IRS. This, though, seems a stretch. Even if it is true, it means that the returns do contain something Mr Trump would rather not reveal.

Mr Trump’s critics, most notably Mitt Romney, have called for him to release past returns that the IRS has finished scrutinising. For most people, IRS audits stretch back no further than six years. Mr Trump has said little more about what time period the audit relates to, other than it goes back a while and that he has been audited continuously for 12 years.

It is unclear where Mr Trump’s initial timeline for releasing his returns came from: IRS audits can be time-consuming, sometimes taking over two years from the date on which takes were filed. The forecast of “three [or] four months” may have just been a ploy to buy time until Mr Trump had the Republican nomination sewn-up. Though Hillary Clinton can attack Mr Trump’s financial secretiveness in the general election, voters perceive her as comparably untrustworthy to Mr Trump. Coming from her, an allegation that Mr Trump has something to hide is less potent.

What is Mr Trump keen to keep secret? It could be that he is less rich than he boasts. Or it could be that he pays little tax—although he takes pride in trying “very hard to pay as little tax as possible”. In early 2015 Mr Trump said that were he to run for president, he would release his tax returns, and he would “also explain to people that as a person that’s looking to make money, I’m in the business of making money”, hinting that early on he sensed the public might be uneasy about the small size of his tax bill. Or the returns could contain some other embarrassment, like Mr Trump somehow making use of the carried-interest tax loophole, beloved of hedge-fund managers, that he promises to abolish, or that he gives little to charity.

In any case, Mr Trump, for now, responds to questions about his tax rate by saying it is “none of your business”. Given Mr Trump’s ability to withstand—and capitalise on—public outrage at his behaviour, that he is resisting releasing the returns is a strong signal that they contain some bombshell. Two-thirds of voters think he should release his returns, but how much they care is unknown (there is some evidence from other countries that voters care about financial transparency, which we explored in a recent article, though in many countries politicians do not routinely release their tax returns). Keeping the returns private leads to continued negative coverage for Mr Trump. But that is probably better than the heat of a scandal.