The White House is offering another rationale for why Democrats should not get their hands on President Donald Trump's tax filings: They're not "smart enough" to properly understand them.

Speaking with "Fox News Sunday" host Chris Wallace, White House press secretary Sarah Sanders said she wouldn't "trust" members of Congress to fully grasp the contents of the president's returns.

"And frankly, Chris, I don't think Congress, particularly this group of congressmen and women, are smart enough to look through the thousands of pages that I would assume President Trump's taxes will be," Sanders said. "My guess is most of them don't do their own taxes, and I certainly don't trust them to look through the decades of success the president's had and determine anything."

Sanders said Trump has "been clear since the beginning that as long as his taxes are under audit he's not going to release them" and has "also filled out hundreds of pages in financial disclosure."

Asked if Trump will order the IRS not to release his filings, Sanders said, "We'll have to see what happens on that front."

Sanders' remarks come after congressional Democrats gave the IRS an April 23 deadline to turn over the president's returns to the chairman of the House Ways and Means Committee. Earlier this month, the committee's chairman, Richard Neal, D-Mass., formally requested six years of Trump's personal and business tax filings from the IRS under a statute that allows him to demand an individual's returns. That statute allows the chairman to request the returns for a policy-related purpose, and Democrats have insisted they need to see the taxes to determine how Trump's financial interests might be influencing his policymaking decisions.

The Treasury Department initially rebuffed an April 10 deadline Neal set. Should the IRS not turn over the returns, it could spark a legal battle to obtain them.

"To date, the IRS has failed to provide the requested return and return information despite an unambiguous legal obligation to do so. ... Please know that, if you fail to comply, your failure will be interpreted as a denial of my request," Neal wrote in a letter to IRS Commissioner Charles Rettig, adding there was "no valid basis to question the legitimacy of the Committee’s legislative purpose."

Speaking about the latest request, Treasury Secretary Steve Mnuchin said Saturday that as he has "emphasized in the past, I think the request raises some very complex issues."

"And I do intend to follow the law, but I think these raise very, very complicated legal issues," he said. "I don’t think these are simple issues."

Trump spoke about the request Wednesday, telling reporters he's not going to make his taxes public because they're under audit.

"No, there is no law," he said. "As you know, I got elected last time with this same issue. And while I’m under audit, I won’t do it. If I’m not under audit, I would do it. I had no problem with it. But while I’m under audit, I would not give my taxes. There’s no law whatsoever.

Trump has been saying he is under audit since the 2016 election cycle, using that explanation to refuse to release his returns. Although the IRS has regularly audited presidents and vice presidents since the 1970s, being under audit does not preclude Trump from making the information public. Trump is the only major presidential candidate of either party since the early 1970s not to release his tax returns.

Last Sunday, acting White House chief of staff Mick Mulvaney said Democrats will "never" be able to obtain Trump's taxes.

Sanders on Sunday said the Democrats' request "has nothing to do with whether they're going to determine policy" and said Democrats were going down a "dangerous, dangerous road," calling the move "disgusting overreach."