Served with a proper demand by Representative Richard Neal, the Ways and Means Committee chair, Treasury Secretary Steven Mnuchin responded, “I have determined that the Committee’s request lacks a legitimate legislative purpose,” and that he therefore would not comply.

Let’s begin at the beginning: To paraphrase Joe Pesci in My Cousin Vinny, Section 6103 is what we lawyers call a “statute.” It was adopted by Congress as part of the Tax Reform Act of 1976. The final Senate vote on the bill was 81–1; in the House, it was 405–2. It was signed by President Gerald Ford (for those scoring at home, a Republican). Under the United States Constitution, Article VI, Section 2, it, like all statutes, is “the supreme law of the land.” It contains no provision requiring a “legislative purpose” at all. That’s not an oversight. Congress isn’t always legislating. It has other functions; one of them is to investigate officials and even private citizens, which has been part of Congress’s mission since its 1790 inquiry into the financier Robert Morris’s management of federal revenue during the Revolution.

I can’t find any mention of “legislative purpose” in the statute’s legislative history; the Senate report notes only that congressional committees “would continue to have access to returns and return information.” Nor is “legislative purpose” mentioned in the two Office of Legal Counsel opinions I have found that deal with disclosure of returns to congressional committees. “While Congress was concerned about the citizens’ right to privacy, it was also concerned about the Government’s need for the tax information, and was very much aware of its own needs,” an opinion stated in 1977. “The legislative reports, in addressing this issue, simply state that the committees will have access to tax information ‘upon written request of their respective chairmen.’”

Finally, the text contains no provision empowering the secretary of the Treasury to determine whether such a request is “legitimate.” It says “shall furnish.” The lawful response is, “Here they are.” The lawless answer is, “I personally don’t think you have a good reason to ask.” A private citizen who gave such an answer to a lawful order would be headed for jail.

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Mnuchin’s defiance is of a piece with the administration’s utterly unprecedented claim that “executive privilege” permits it to refuse to provide documents or testimony whenever it suits the president. Though not mentioned in the Constitution, executive privilege over the years has evolved to protect a few classes of information—military and law-enforcement secrets, for example, specific advice provided by officials directly to the president, and certain internal deliberations over policy.

But except in those limited cases, the executive is expected to provide information at the request of Congress and the courts. Sometimes these disputes require negotiation to reach a balance between what Congress seeks and what the president feels able to reveal. Since the George Washington administration, the most common result has been compromise; though sometimes the fight turns ugly, as former officials such as Attorney General Eric Holder and White House Counsel Harriet Miers found out when different Congresses held them in contempt for defying subpoenas.