(CNN) President Donald Trump has been consistent about very few things during his relatively-short political life. But on one front he has been adamant: He will not release any of his past tax returns.

That position became slightly less tenable on Tuesday when The Washington Post reported on the existence of a 10-page draft memo from the Internal Revenue Service that makes clear the administration has no leeway when it comes to complying with a request for Trump's returns from House Ways and Means Chairman Richard Neal, a Massachusetts Democrat.

The memo says that the turnover of Trump's tax returns "is mandatory, requiring the Secretary (of the Treasury) to disclose returns, and return information, requested by the tax-writing Chairs" and adds that the IRS statute "does not allow the Secretary to exercise discretion in disclosing the information provided the statutory conditions are met."

That assertion runs directly counter to Treasury Secretary Steve Mnuchin's recent refusal to comply with a 1924 statute that says he "shall furnish" any individual American citizen's tax returns to the heads of the House and/or Senate tax-writing committees. Mnuchin denied Neal's request by citing the fact that he found no legitimate legislative purpose for the Ways and Means chairman to ask for the returns. In a letter to Neal earlier this month, Mnuchin wrote that he and the Treasury Department's lawyers believe that "the Committee's request lacks a legitimate legislative purpose."

This memo, which was prepared by the IRS last fall, badly undercuts that argument. It clearly states that Mnuchin has zero discretion in the matter under the law; if Neal asks, Mnuchin needs to comply.

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