News events have diverted attention from the issue of Donald Trump’s tax returns for several weeks, but it’s an important issue that will come back, which is why you should read this article now. Reporter and tax expert David Cay Johnston uncovered two tax cases from the 1990s in which Trump filed appeals and lost. The cases show that at least in 1984, he paid no income tax at all, and one of the cases suggests some decidedly odd behavior.
A tax lawyer and accountant who prepared Trump’s tax returns for over 20 years testified, when shown Trump’s 1984 return, that he and his firm did not prepare it. Yet he acknowledged that the signature on the photocopy was his. How might that have happened? The judge stated that the original return was never found.
The bigger issue is that Trump has promised to release his tax returns but hasn’t done so, and it isn’t clear why not. He has said he wants to wait until audits are resolved, but why? Johnston observes that “a tax return is filed under penalty of perjury and releasing a return has no effect on an audit, as many tax authorities (including a former IRS commissioner) have noted.”
Until he releases his returns or offers a plausible reason not to, voters must speculate on why he’s withholding them. None of the potential reasons will be good. Hillary Clinton is in a strong position to pound him on the issue, since she and her husband have routinely released their returns for years (though she may not want to remind voters of her speaking fees from Goldman Sachs). The media will keep digging. Trump has eluded the issue so far, but it will come back to bite him.
This essay appeared in Power Sheet, Fortune’s daily newsletter on leaders and leadership. Sign up here.