Donald Trump won’t release his tax returns. This is what they could reveal.

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• JUDY WOODRUFF:

  And we turn now from foreign policy to an issue that continues to grab headlines in the campaign: Donald Trump's taxes and so far his refusal to make them public.

  Hillary Clinton says he must be hiding something, while Trump himself has pledged to release them, but only when IRS is finished its audits. That is something that can last seven years.

  We want to get past all these headlines.

  And our Lisa Desjardins helps put it all in context.

• LISA DESJARDINS:

  Let's start with basic facts.

  So far, Donald Trump has not made his tax returns or summaries on them public. And he gives a consistent explanation.

  DONALD TRUMP (R), Presidential Nominee: And I am under audit, a routine audit. And when the audit is complete, I will release my returns. I don't know when that is going to be. But when the audit is complete, I will release my returns. I have no problem with it. It doesn't matter.

• LISA DESJARDINS:

  But this is his choice. The IRS confirmed this year that nothing prevents Trump, or any of us, from releasing personal tax returns anytime.

  Now, most of us don't have the 1,000-page tower of returns that Trump tweeted about last year, but that's important. You see, Trump's personal taxes are also the taxes of his company. The Trump Organization, with its 500 associated companies, files as a kind of family business, whose dealings are taxed as Trump's personal income, which brings us to the bigger point: What could Trump's taxes tell us?

  A lot. How successful the businessman actually is, what ties does he have abroad, how his companies operate there, if and how much he gives to charity, and whether Trump pays any taxes at all. Trump likes to bring that up himself.

• DONALD TRUMP:

  I pay as little as possible. I fight like hell to pay as little as possible for two reasons. Number one, I'm a businessman. And that's the way you're supposed to do it.

• LISA DESJARDINS:

  Now to perspective. How unusual is Trump's refusal to release? In modern politics, he is alone. Since 1980, every president from Ronald Reagan to Barack Obama has released their returns publicly. And so has each nominee.

  John McCain released the fewest, two years of returns. Hillary Clinton has released the most, 39 years of returns. But was anyone else under audit? Yes, Richard Nixon.

  RICHARD NIXON, Former President of the United States: People have got to know whether or not their president is a crook. Well, I'm not a crook.

• LISA DESJARDINS:

  Nixon wasn't talking about Watergate there. He was talking about his finances after an IRS audit in 1973 showed he owed more than $400,000 in back taxes. Nixon eventually released four years of returns, sparking the modern tradition.

  Another option for Trump, like fellow billionaire politician Michael Bloomberg, Trump could release a summary, or the first pages of his taxes. Or he could he release the taxes that have completed audits, those up to the year 2008. His response?

• DONALD TRUMP:

  The only one that cares is the press, I will tell you. And even the press, I tell you, it's not a big deal.

• QUESTION:

  You don't think there are voters out there who…

• DONALD TRUMP:

  I don't think so, no. I think people don't care.

• LISA DESJARDINS:

  But is that true? Actually, a recent poll found two-thirds of likely voters think seeing candidates' tax returns is important.

  And, in this election, two-thirds of voters don't agree on much.

  For the "PBS NewsHour," I'm Lisa Desjardins.