Neal, a Massachusetts Democrat, sent a second letter to the Internal Revenue Service on Saturday, asking for six years of Trump’s personal and business returns, citing a section of the tax code that allows the chairman of the tax committees to request the returns of any taxpayer, including the president.

“I am aware that concerns have been raised regarding my request and the authority of the Committee,” Neal wrote. “Those concerns lack merit.”

There is “no valid basis” to question the legitimacy of the Ways and Means Committee’s legislative purpose, Neal added.

The letter signals that Neal could be preparing to issue a subpoena or take other legal action, including a lawsuit, to compel officials to obtain and turn over the president’s returns. That would set up a protracted legal battle between the Trump administration and House Democrats that could span beyond the 2020 presidential elections.

Needs More Time

Neal sent a letter earlier this month to IRS Commissioner Charles Rettig asking that the returns be turned over by April 10. Treasury Secretary Steven Mnuchin responded by the deadline saying he needed more time to review the request and consult with the Department of Justice.

In that letter, Mnuchin also questioned the scope of Congress’s investigative authority and Neal’s stated reason for the request — that he wants them to insure that the IRS is properly auditing presidents.

Federal law gives the chairmen of House Ways and Means, Senate Finance Committee and the Joint Committee on Taxation the power to request the returns of any taxpayer, although some legal scholars believe the request needs a legitimate legislative purpose, which Democrats say they have met.

Members of the Trump administration, including acting White House Chief of Staff Mick Mulvaney, and their allies have called the request a political attack and a violation of Trump’s privacy.

The House Democrats’ asked that the returns be turned over to the members of Congress. They would then decide whether to release them publicly, but the political pressure among Democrats to do so would be high, as would the resistance among Republicans.

Trump broke with 40 years of presidential campaign tradition by declining to release his personal returns before the 2016 election. He said that he was under audit and didn’t intend to turn anything over until that process had been completed. There is no prohibition on releasing returns to Congress or the public while under audit.

“It pisses the members off if you don’t give them information that they think they should have. But for lawmakers, there’s no real effective remedy except to say bad things about them or not take their phone calls,” said Christopher Rizek, a former Treasury official who is now a tax litigator at law firm Caplin & Drysdale. “People expect the rule of law to work smoothly, but that”s not always the case.”