AS CONGRESS voted on major tax-cut legislation, White House press secretary Sarah Huckabee Sanders on Tuesday was peppered with questions about how the overhaul of the tax code would affect President Trump. She defended the president's claim that the bill will "cost me a fortune" but allowed as how "on the business side" he might benefit. "This actually could impact the president in a large way," she said when pressed about the matter.

Exactly how the president would benefit personally from legislation he pushed — and soon plans to sign into law — is something the American public has a right to know. That it continues to remain in the dark is due, of course, to Mr. Trump's refusal to release his tax returns and Congress's complicity in failing to insist on a minimal degree of openness from the executive.

Mr. Trump's lame excuse that he can't release his tax returns because he is under audit by the Internal Revenue Service was trotted out once again by Ms. Sanders. The IRS has made clear that an audit is not a bar to someone releasing their returns. Indeed, President Richard Nixon released his returns in 1973 when he was under audit.

Mr. Trump is the first president in 40 years to hide his returns, which would provide critical information about his finances, including any conflicts of interest or foreign influence. It's not hard to guess why. Evidently, he believes the fallout from the information contained in the returns would be worse than the criticism he receives for withholding them.

A case in point is the tax bill: The White House billed it as helping middle-class Americans and claimed Mr. Trump would be a "big loser." In fact, as experts have pointed out, Mr. Trump and his family are likely to reap immense rewards from a lower top tax rate, a lucrative new deduction for the "pass-through" businesses he controls and changes to the estate tax. Tax authorities told The Post's Drew Harwell that, thanks to a last-minute adjustment of the new deduction for pass-through businesses, real estate, rental and leasing companies such as Mr. Trump's will benefit more than any other. So much for the populist spin about middle-class Americans.

"It's so clear that he is financially much better off than previously," said Daniel Shaviro, a tax professor who worked for Congress's Joint Committee on Taxation during the last big tax overhaul in 1986. "I'd be at a loss as to how they could even dare to argue" otherwise. In fact, "they" dare to do so because as long as the facts of Mr. Trump's finances and taxes are hidden, they think they can get away with it. And sad to say, so far they are right.