The chairman of the House Ways and Means Committee recently disclosed that he received a whistleblower allegation of "inappropriate efforts to influence" the IRS tax audit of President Donald Trump.

Experts and former investigators told Insider the complaint could be the tipping point in the battle between House Democrats and Trump over obtaining his tax records, which he has long sought to hide.

The White House is grappling with another whistleblower complaint, which alleges that a phone call in which Trump pressured Ukraine to investigate a political rival violated the law.

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With Washington, DC, embroiled in the fallout from a whistleblower's revelations that President Donald Trump pressured Ukraine's president to investigate a Democratic rival, another whistleblower scandal has received scant attention.

But experts say the second complaint could prove just as damaging for the president as the Ukraine controversy.

In a letter recently filed as part of his bid to obtain six years' worth of the president's tax returns, the chairman of the House Ways and Means Committee, Rep. Richard Neal, wrote that he received a credible complaint from a whistleblower at the end of July.

The complaint, Neal wrote, alleges "inappropriate efforts to influence" the IRS audit of Trump's tax returns.

At this stage, details are sparse. The identity of the whistleblower is unknown, as are the specifics of the complaint.

Experts and former prosecutors told Insider the complaint could land the president in legal jeopardy — and, just as important, lead to the release of the tax returns Trump has long shielded from public view.

Neal's bid for Trump's tax returns has exasperated some Democrats who say it's been too modest and slow-moving. Instead of making a sweeping bid for information on the president's financial affairs, Neal made the narrower request that Congress be granted oversight of the IRS audit.

Trump and President Richard Nixon. Justin Sullivan/Getty Images, Charles Tasnadi, File/AP

Not much is known about the process of auditing a president. Rules governing it were tightened after President Richard Nixon was accused of influencing the process.

"One of the things that came out of Watergate was that he and his office had tried to use the IRS to go after political enemies," Patrick Cotter, a former federal prosecutor who was part of the team that convicted the Gambino crime family boss John Gotti, told Insider.

In the wake of the scandal, Congress enacted a law making it a crime for any member of the executive branch to cause or terminate an IRS audit.

Because presidential candidates have voluntarily released records in the past several decades, the executive audit process has received little attention since Nixon.

But Neal argued in his filing that the existing guidelines are insufficient because of the vast powers of the presidency and that the president's tax records therefore need congressional oversight.

If Neal's demand is granted, he'll be given access to the president's tax records, which opponents believe could expose wrongdoing by Trump.

The Treasury Department has so far blocked Neal's request, arguing that the Massachusetts Democrat isn't seeking oversight for sound reasons, but in an effort to damage the president's reputation.

Trump has been at the center of several financial scandals. The New York Times reported last year that Trump used a series of dubious tax schemes to shield a $400 million inheritance from the IRS.

And in September, Mother Jones published an investigation that found that Trump might have fabricated a loan to avoid paying $50 million in income taxes.

But Trump has long maintained that he has committed no financial or tax crimes. He has said he can't release his tax returns because they are under audit, even though there is no rule to prevent him from doing so.

Democratic Rep. Richard Neal. Toya Sarno Jordan/Getty Images

Daniel Shaviro, the Wayne Perry Professor of Taxation the New York University Law School, told Insider that the new whistleblower complaint tipped the balance in Neal's favor in his struggle to obtain Trump's tax records.

"Specific grounds for concern about audit interference would appear to me to make the legal case for discovery [of the tax records] overwhelming," he said in an email, adding that he considered it "exceptionally strong even without the complaint."

But despite the strength of the case and the whistleblower's evidence, Neal's attempts could get bogged down in legal disputes, Shaviro said.

"The wild card here is that we don't know how partisan judges who view themselves as loyal Republicans will respond even to clear legal issues," Shaviro said.

There could be other obstacles for Democrats. It's unclear whether the whistleblower complaint implicates Trump in breaking the law, or in a more minor fault.

Cotter said that if someone in the executive branch tried to cause or terminate the audit on Trump, the vice president, or anyone else, it would be a felony.

He also pointed to a potentially applicable tax-evasion statute making it a crime to intentionally try to evade paying fair taxes.

"If you tried to interfere with an audit — the way that normally happens is people lie," he said. "So if someone were trying to interfere with an audit — and of course one of the purposes of the audit is to try to figure out how much you owe and collected — then you could be prosecuted for tax evasion."

It's also possible the complaint contains details about efforts to delay the mandatory IRS audit of Trump's tax returns.

"It's required that Trump be audited as president, and that should have happened years ago, within the first few days he took office," said Jeffrey Cramer, a longtime former federal prosecutor who spent 12 years at the Justice Department.

"We know Trump's in no hurry to get the audit done, because when that's finished, his excuse that he can't release his tax returns is finished too.

"So one question worth asking is: Has the Treasury Department or IRS done what they were required to do and audited the president and vice president?" he added. "Or is it possible Trump's audit is being slow-walked?"

The complaint could also pertain to the actual handling of the documents.

"The president's and vice president's tax returns are kept in a top-secret vault," Cramer said. "It's codeword-protected, the whole nine yards, and not just anyone can get in there. There are very few people — the head of the Treasury, the head of the IRS — who have access."

Cramer noted, however, that many of the details about the complaint are still murky.

"Someone may have taken the official whistleblowing steps to file this, but it could just as easily be a pissed-off IRS employee in Washington, DC, talking to a committee staffer," he said.

And even if Neal does obtain the mysterious tax records, will they prove as damaging as many critics believe they could?

Steven M. Rosenthal, a senior fellow at the Urban-Brookings Tax Policy Center in Washington, has testified before the Ways and Means Committee about what Trump's tax returns might reveal.

He said they could provide answers to long-standing questions about whether Trump is involved in murky financial entanglements with foreign oligarchs. The information could strengthen the hand of Democrats seeking impeachment.

"What you might find are things like: Does the president have foreign accounts? Does the president have foreign partners? Does the president have foreign-sourced income, and from where?

"All of that might be important to unraveling whatever foreign entanglements the president has and continues to have by virtue of operating a global business," he told Insider in an interview.

He said they also "might become used for purposes other than those" of oversight that Neal wants them for.

"They might be used to fill in the pieces of the puzzle — the puzzle of Trump, Trump's financial operation," he said.