For three days now, Donald Trump has been the official nominee of the Republican party.

For many decades now, almost all major party nominees have released their federal income tax returns, as part of the implied bargain of running for president. The bargain is this: candidates are asking the public to grant them the enormous discretionary powers of the presidency. (Yes, presidents get frustrated by what they can’t do. What they can do is still vast.) In exchange, the public asks to know as much as it can about the person assuming this role.

So major-party nominees in modern times have released some version of their medical records, and their federal tax returns. You can see the returns for presidents going back to FDR here. (FDR’s records, which were released after his death, start in 1913 — which was when the Sixteenth Amendment first authorized the income tax!). Nominees began routinely releasing records before the elections in the 1970s. You can see the history of modern-era Republican returns here.

Donald Trump has flat-out refused to accept this obligation. “Flat-out” in the sense of telling George Stephanopoulos in May that the returns were “none of your business,” your meaning the press’s and public’s; and less directly in saying that the ongoing-audit status of the returns means he can’t disclose them. (No actual tax expert agrees.)

Is there something embarrassing or explosive in Trump’s tax returns? Who knows. Geoff Colvin, of Fortune, suggests that there might be. Many people have speculated that the real embarrassment might be evidence that Trump is nowhere near as rich as he has claimed. Another hypothesis is that returns would show that he has given very little to charities, or has managed to pay no taxes at all. The real point is that all of these remain hypotheses, as long as Trump shirks an obligation that modern-era candidates have recognized. As Colvin says:

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

Now that he is officially the nominee, the press, his opponents, and for that matter his supporters as well should ramp up insistence that he do what nominees over the past half century have done.

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