Trump is seen above the floor of the New York Stock Exchange in June 1995 after taking his flagship Trump Plaza Casino public in New York City. (AP Photo/Kathy Willens, File)

When the topic first came up, Donald Trump's excuse for not releasing his tax returns was a vague one. "I'm thinking about it," he told ABC's George Stephanopoulos in October. He also repeated a line he rolled out in August on "Face the Nation": Maybe he'd release his tax returns when Hillary Clinton released her emails.

Clinton's emails are now out (though your definition of that may vary), and still no Trump returns. Last month, the excuse changed. Now, it was that Trump was being audited, as he is every year, and that he wouldn't release his returns while they were under audit. (The IRS pointed out that there was no legal reason not to, but a tax attorney we spoke with agreed that it wasn't the smartest thing to do.)

This week, CNN's Anderson Cooper asked if Trump would release the letter from the IRS letter proving that he was under audit. Trump agreed, but on Wednesday he released a statement on the letterhead of his tax attorney.

(FUN FACT: Trump's tax counsel is Morgan, Lewis & Bockius, the firm employing the attorney that Lois Lerner tapped to ask her at a conference about audits of 501(c)(4) organizations -- crumbling the dam holding back the 2013 IRS scandal.)

The core contention of the letter is that Trump's "tax returns for the years 2002 through 2008 have been closed administratively by agreement with the IRS without assessment or payment, on a net basis, of any deficiency." What does that mean? Can Trump release those returns now, or what?

To find out, we got in contact with Mark Everson, one-time long-shot 2016 Republican presidential candidate and -- more importantly for our current purposes -- former commissioner of internal revenue at the IRS.

To cut to the chase: No, this letter offers no reason why Trump can't at least release his returns from 2002 to 2008 -- and maybe more recent ones, too.

Everson makes several points.

First, he points out that the letter notes the 2002 to 2008 audits were closed without any assessment or payment -- indicating that Trump filed all of the taxes he owed.

"Well, bravo for Mr. Trump!" Everson said. "That's a great result! And if that's the case, certainly one would say, why wouldn't you release those returns?" After all, the IRS looked at those returns, said that Trump was fine, and closed the files.

In the past, Trump has implied that his attorneys wouldn't let him release returns while he was being audited (see here, for example). If Trump were worried about releasing returns that are being audited for the same reason a crime suspect might not talk to the press while the cops are searching his apartment, now that the suspect has been cleared of suspicion, there's no reason not to. What's more, as Everson notes, the attorneys don't say anything about not releasing his returns while they're being audited.

Second, Trump's sprawling business empire likely hasn't changed much since 2008 -- meaning that his 2009 through 2014 filings probably don't differ too much from the previous ones.

"The IRS -- the people there aren't knuckleheads in terms of using their time," he said. "If they look at something in the years 2005 and 2006 and the treatment is proper, in my view they're not going to look at it again in 2010 and 2011."

"If there's no net assessment, presumably there's somewhat limited risk to Mr. Trump, and those reasons for not making disclosure [of the earlier years] are political rather than exposure to risk from a tax perspective," Everson said.

If Trump is withholding his returns from 2002 to 2008 for political purposes, we're back into the realm of speculation. Why would he want to hide his returns? Is this a situation like his overseas manufacturing, where he took advantage of legal loopholes that might cast him in a negative light? Did he successfully shield himself from having to pay any federal income tax at all? As it stands, we'll likely never know.

That Trump wouldn't turn over his tax documents -- and that Ted Cruz would use that as cover to only release a summary document -- is clearly frustrating to Everson.

"He agreed to [release his taxes] when he agreed to be a candidate. That's the transparency. That's the expectation," Everson said. "It may not be written into law, but that's an expectation that's been established as part of the contest. He ran and secured votes over a period of months, saying that he would release the returns."

It could be written into the law, he says. Congress could pass a bill mandating the release of tax returns for major candidates, as there is a mandate to report campaign spending. (Would this Congress pass it? Would the Supreme Court uphold it? Those are different questions.)

"Clearly, he had second thoughts about what's in the returns and whether he wants that out; that much is very clear," Everson said.

What isn't clear is whether or not his opponents or the public have any leverage over his actually releasing them.