(Bloomberg Opinion) — The White House’s fierce response to the impeachment inquiry by the House of Representatives, calling the enterprise “an unconstitutional effort” and a violation of “constitutionally mandated due process,” seems to make one commitment: noncooperation.The key sentence in the eight-page letter, signed by White House counsel Pat A. Cipollone, is this: “Given that your inquiry lacks any legitimate constitutional foundation, any pretense of fairness, or even the most elementary due process protections, the Executive Branch cannot be expected to participate in it.”What can the House do in response?Let us step back a bit. No White House welcomes a congressional investigation, and an impeachment inquiry is the least welcome of all. Any White House counsel has a duty to protect the president and the presidency (and, if necessary, to do so fiercely). Under both Democratic and Republican presidents, congressional investigations, including scandal-mongering, are often efforts to score political points by obtaining internal documents that may well be protected by executive privilege (which safeguards the confidentiality of presidential conversations).So the White House’s reluctance to hand over documents is hardly unusual. What is unusual is the sweeping vow of noncooperation and this wild objection: “you have denied the President the right to cross-examine witnesses, to call witnesses, to receive transcripts of testimony, to have access to evidence, to have counsel present, and many other basic rights guaranteed to all Americans.”An impeachment inquiry is hardly a criminal trial. In fact, it is not a trial of any kind. In a congressional hearing, whether open or closed, members of Congress typically call witnesses and ask them questions. There is no cross-examination. Does the White House counsel really want the president of the United States or his lawyers to be able to cross-examine and call witnesses? What does that even mean?Does the White House counsel think that the U.S. Constitution guarantees that right, in the context of an impeachment inquiry?The House has already issued a subpoena, specifically focusing on the White House’s interactions with Ukraine. Compliance with a lawful congressional subpoena is not optional. The House can go to court and attempt to get the subpoena enforced. Alternatively, it can hold the recipient in contempt of Congress (that’s a misdemeanor, with a jail sentence).The largest response, of course, is an article of impeachment. There is precedent for that. During the Watergate affair, a majority of the House of Representatives voted in favor of this article:In his conduct of the office of President of the United States, Richard M. Nixon . . . has failed without lawful cause or excuse to produce papers and things as directed by duly authorized subpoenas issued by the Committee on the Judiciary of the House of Representatives on April 11, 1974, May 15, 1974, May 30, 1974, and June 24, 1974, and willfully disobeyed such subpoenas. The subpoenaed papers and things were deemed necessary by the Committee in order to resolve by direct evidence fundamental, factual questions relating to Presidential direction, knowledge or approval of actions demonstrated by other evidence to be substantial grounds for impeachment of the President.Notably, the article added that Nixon was “substituting his judgment as to what materials were necessary for the inquiry” and thus “interposed the powers of the Presidency against the lawful subpoenas of the House of Representatives, thereby assuming to himself functions and judgments necessary to the exercise of the sole power of impeachment vested by the Constitution in the House of Representatives.”For an article of impeachment to be based on defiance of a subpoena, it would be best, of course, if a federal court had concluded that the president’s disobedience was in fact unlawful. But that can take a long time.Moreover, it is a fair question whether and when defiance of a subpoena, as such, amounts to a high crime and misdemeanor within the meaning of the Constitution’s impeachment clause. If a subpoena does not involve a matter of great importance – if it involves, say, alleged misconduct by low-level officials at the Department of Agriculture – it would be very difficult to justify impeachment. And if a White House believes, reasonably and in good faith, that a subpoena is unlawful, it would be hard to argue that disobedience is impeachable.But in this case, there is no question that the subpoena involves a matter of great importance. Whether the White House reasonably believes that it is unlawful depends on what, exactly, it is asking for.That’s why its categorical refusal to cooperate is difficult to defend. Under normal circumstances, Cipollone’s over-the-top letter would be an opening salvo – the first step in a negotiation. But, to say the least, these aren’t normal circumstances.To contact the author of this story: Cass R. Sunstein at firstname.lastname@example.orgTo contact the editor responsible for this story: Katy Roberts at email@example.comThis column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.Cass R. Sunstein is a Bloomberg Opinion columnist. He is the author of “The Cost-Benefit Revolution” and a co-author of “Nudge: Improving Decisions About Health, Wealth and Happiness.”For more articles like this, please visit us at bloomberg.com/opinion©2019 Bloomberg L.P.