Donald Trump returned to a familiar excuse for not releasing his tax returns Monday night: He is under a "routine audit."
But the Internal Revenue Service has said that nothing precludes someone under audit from releasing his or her tax returns.
In the debate, Trump said much information could be gleaned by the financial disclosures he submitted earlier this year. But as Hillary Clinton pointed out, only the tax returns would reveal Trump's charitable giving and the marginal tax rate he has paid.
Clinton suggested Trump effectively paid zero income tax, a charge Trump did not specifically rebut but interjected, "That makes me smart."
He is the first presidential nominee in 40 years to refuse to release his taxes. (President Gerald Ford issued only a summary when he sought re-election in 1976.) By contrast, Clinton has released decades' worth of returns.
Trump did suggest Monday that he would release his taxes in exchange for Clinton releasing the 33,000 emails that he alleges were deleted from her private email server while she served as secretary of State.
While Trump has repeatedly attacked Clinton for a lack of transparency, he has been far more secretive than his presidential rival _ and every other major-party candidate in recent history.
Trump has provided only the barest details about his personal health. Clinton, after initially hiding a diagnosis of pneumonia, has released a more extensive health evaluation from her personal physician.
Trump has declined to document the tens of millions of dollars he claims to have donated to charity, even as extensive reporting by The Washington Post has contradicted those claims.
Separately, an organization that tracks nonprofits, GuideStar, examined the Bill, Hillary and Chelsea Clinton Foundation and found it has been far more transparent than the Donald J. Trump Foundation.
GuideStar said the Clinton Foundation tracks its philanthropic programs to determine how many people around the world are benefiting, such as women receiving job training. Such analyses make it "far easier for donors and citizens to meaningfully analyze the institution's value to society," GuideStar said.
The Trump Foundation provides no such data.
The report also said it appeared that the Clintons had donated more money to charity _ largely through their foundation _ than Trump. However, the figure is impossible to know for certain because Trump has declined to release his tax returns.
