Washington (CNN) President Donald Trump continues to say he's under audit and can't release his taxes after House Democrats formally requested his tax returns from the IRS.

On Wednesday, the Democratic chair of the House Ways and Means Committee used a nearly century-old law to make the request, which could trigger a protracted legal battle over the President's tax returns.

Trump offered his first response at a White House event later that day: "Now, we're under audit, despite what people said. We're working that out. I'm always under audit, it seems. But I've been under audit because the numbers are big, and I guess when you have a name you're audited. But until such time as I'm not under audit, I would not be inclined to do that."

Asked again on Thursday, Trump said the IRS commissioner would need to "speak to my lawyers and speak to the attorney general."

Facts First: No matter what Trump says, an audit would not prevent him and has not stopped past presidents from releasing their tax returns.

Here's where it gets tricky. Trump's personal tax returns are likely under audit, but it's not exactly what you suspect.

Every year dating back to the early 1970s, the Internal Revenue Service has made it a regular practice to audit the personal tax returns of every sitting US president and vice president.

The decades-old practice began shortly after President Richard Nixon and Vice President Spiro Agnew were both embroiled in tax scandals during the Watergate era. It was then that Nixon famously told reporters in November 1973, "People have got to know whether or not their President is a crook. Well, I'm not a crook." Nixon and Agnew both ultimately resigned from office.

But Nixon went so far as to invite the Joint Committee on Taxation to examine his returns while the IRS conducted its own review. (Democrats have pointed out that this debunks Trump's claim that he can't release his taxes during an audit, and his claim that nobody has ever done it.)

After that move from Nixon, though not legally required to do so, it became commonplace for subsequent presidential candidates and commanders-in-chief to release their tax returns to the public.

Then came Trump, who in 2016 became the first major candidate to refuse, citing an ongoing audit. He pushed back, saying "nobody cares" about his finances. He even said, without evidence, that the IRS might be targeting him "because of the fact that I'm a strong Christian."

Technically, there's nothing preventing Trump from releasing his tax returns now. Most tax attorneys would typically advise a client against doing so if they're under audit to avoid further scrutiny. Once the tax returns are out, reporters could find something that the IRS missed. Of course, most tax attorneys don't represent presidents or people running for the White House.

Regardless of those risks, past presidents released their tax returns while in office. Presidents Barack Obama and George W. Bush both did during their tenure. (But neither of them led a sprawling business empire like Trump, who is involved in approximately 500 corporate entities.)

During the campaign, Trump's attorney and fixer Michael Cohen told reporters that Trump was under audit and therefore could not allow the returns to be released.

"I personally will not allow him to release those tax returns until the audits are over," Cohen told CNN in August 2016. "There is not a lawyer on this planet that should give that advice -- any advice other than what I just gave -- to their client short of suffering malpractice."

But times have changed. Cohen is now a convicted felon and flipped on Trump, offering testimony to special counsel Robert Mueller and other prosecutors about Trump's supposed misdeeds. This all came to a head in February when Cohen publicly testified on Capitol Hill.

During the dramatic hearing before the House Oversight Committee, Cohen further questioned the existence of the President's audit. He told lawmakers that he asked Trump for a copy of the audit, so he could discuss the subject with reporters, but he "was never able to obtain one."

"Statements he made to me ... what he didn't want was to have an entire group of think tanks that are tax experts run through his tax return and start ripping it to pieces, and then he'll end up in an audit and he'll ultimately have taxable consequences, penalties, and so on," Cohen explained to California Democrat Rep. Jimmy Gomez when asked about Trump's tax audit.

Gomez followed up to ask if Trump was not actually under audit at the time?

"I presume that he is not under audit," Cohen said.

To be clear, there is no way to definitively verify if Trump was under audit prior to becoming President. The IRS is not permitted by law to disclose if a private citizen is under audit. The only person who can release that information publicly is the individual or their attorney, but without documentation the public would have to take the individual at their word.

During the 2016 campaign, Trump released a letter from his tax attorneys that confirmed he was under audit. But the letter also said the IRS finished reviewing Trump's taxes from 2002 through 2008. Trump did not release his tax returns from those years, even though the audits were over.

(The letter was deleted from Trump's campaign website, but an archived copy is viewable here .)

So, yes, Trump has almost certainly been under audit since he took office in 2017, like every other American president. But we don't know the status of Trump's audits after 2008. And there's nothing legally stopping him from releasing his taxes even if they're being audited.