Former National Security Adviser John Bolton’s unpublished book is the hottest manuscript in Washington. According to a recent story in the New York Times, Bolton provides never-before-public details about events that are at the heart of the ongoing Senate impeachment trial of President Trump—most notably, that Trump directly told Bolton he wanted to maintain the hold on aid to Ukraine until the country announced investigations into the Bidens and supposed 2016 election interference.

During the earlier stages of the impeachment inquiry, Bolton informed the House committees conducting the impeachment inquiry that he would not comply with a subpoena if one were issued because the White House had determined he was absolutely immune from such testimony and had directed him not to comply. But Bolton has now expressed his willingness to testify in the Senate if subpoenaed. And he appears to want to testify, the Times writes—reportedly both because he has relevant information and because he is afraid of the optics of refusing to testify in the impeachment inquiry and then raking in profits from a later-published book about the events.

Republicans arguing against calling Bolton to testify have focused not on the substance of the testimony or the impeachment charges but, rather, on executive privilege. Sen. Ron Johnson, for example, said that he wanted to protect against the “weakening of executive privilege,” and Sen. Lindsey Graham characterized the House as “blow[ing] through these privileges” and insisted he would not “destroy the privilege” by seeking testimony. The president has claimed he would be asserting privilege for the “sake of the office” of the presidency, not his own personal interests, because “you can’t have [Bolton] explaining all of your statements about national security concerning Russia, China and North Korea—everything.”

There are a great deal of questions flying around regarding what would, could and should occur if the Senate subpoenaed Bolton and the president tried to prevent his testimony through executive privilege—and what role, if any, the courts should play and how fast they could settle the dispute if it arose.

The real answer is that no one knows. No president has attempted to use executive privilege to block testimony or evidence in a Senate impeachment trial. There are no Senate precedents dealing with executive privilege in impeachment. And executive privilege itself is so widely disputed and poorly understood that anyone who purports to provide the answer about its operation, particularly in these unprecedented circumstances, is either deluding herself or deceiving everyone else.

There are only analogies, constitutional theories, judicial precedents and historical examples on which to draw to try and discern potential answers or frameworks for decisions. Former executive branch officials, constitutional and congressional scholars, historians, experts on congressional oversight, and journalists approach the question from different perspectives—and many, myself included, have offered their opinion about what could or should happen and how executive privilege should operate in the Senate trial. But these are nothing more than that: opinions, educated guesses and theories, each reflecting, unavoidably, the author’s own background and views.

This is uncharted territory. And the publication of details from Bolton’s draft book pushes the controversy further afield from anything that has previously been seen in this country, even in related contexts such as congressional oversight.

In such a situation, when precedent provides few answers and the stakes are enormously high, the debate should focus on first principles—the fundamental reasons for a particular action or doctrine. But one of the core principles of executive privilege has been lost in the current discussion, particularly when concerns are expressed about “protecting” the presidency or executive privilege itself.

Executive privilege, used broadly, encompasses two related inquiries. On one hand are instances in which a president has determined that the release of specific information would cause concrete, identifiable harm and has refused to provide information because of that harm. On the other hand are instances in which the assertion of the privilege is based on the need to protect generalized institutional interests in confidentiality against undifferentiated harm that could potentially be caused by the prospect of disclosure.

The former inquiry is the form of most historical assertions of privilege. George Washington, for example, withheld some sensitive diplomatic letters between the U.S. minister to France and the French government because the information they contained, if disclosed, could adversely affect the relationship between the U.S. and France. Although the Senate resolution demanding the documents included no express allowance for the president to withhold sensitive letters, Washington’s attorney general explained that “it could scarcely be supposed, even if the words were stronger, that the Senate intended to include any letters, the disclosure of which might endanger national honor or individual safety.”

Similarly, while president, Thomas Jefferson responded to a House resolution requesting information about the conspiracy against the United States involving Aaron Burr by providing all information relevant to Burr but withholding other names. As Jefferson explained: “In this state of the evidence, delivered sometimes, too, under the restriction of private confidence, neither safety nor justice will permit the exposing names, except that of the principal actor, whose guilt is placed beyond question.” And James Monroe refused to provide information about particular charges against a naval officer, reasoning that “the publication of those documents might tend to excite prejudices which might operate to the injury” of the ongoing investigations of the charges against the officer.

There are, of course, many more examples of this constitutional authority, and much debate about how this historical material should be interpreted. But the core of the practice is somewhat clear. As James Madison described it when he was a representative after Washington had refused to provide information to the House of Representatives about a treaty: “[T]he Executive ha[s] a right, under a due responsibility, also, to withhold information, when of a nature that d[oes] not permit disclosure of it at the time. If the Executive conceived that, in relation to his own department, papers could not be safely communicated, he might, on that ground, refuse them ….” In other words, executive privilege exists, in part, to protect against the concrete harm that the disclosure of specific information at a particular time may cause.

There is also a second form of executive privilege, which is currently more common but grounded in a slightly different inquiry. Most modern invocations of privilege do not identify the threatened harm—such as damage to a specific national security interest, a certain diplomatic relationship, a particular ongoing investigation or an individual’s reputation. Instead, they point to the need to protect against damage to undifferentiated, institutional interests, such as the confidentiality of presidential communications (so that presidents and their advisers can speak freely); the confidentiality of internal executive branch deliberations (so that lower-ranking officials can similarly speak freely); or, in the case of President Obama’s assertion over material related to the Fast & Furious investigation, the protection of the executive branch’s internal process in responding to congressional oversight (to prevent unwarranted encroachment by one branch on the other).

Under presidential administrations of both parties, the harm almost every modern assertion of executive privilege protects against has been a generalized institutional harm—an injury to the openness of future presidential and executive branch communications or to the president’s future ability to carry out constitutional responsibilities such as diplomatic relations. That feature makes executive privilege as practiced today similar to evidentiary privileges recognized by the judicial system, such as attorney-client, attorney-work-product or priest-penitent privilege. As a society, we want to encourage free and open communication in those settings, so we recognize them as privileged to further that public interest. But this interest is a general, undifferentiated one. The concern animating a general privilege that protects a particular category of information is not, as it was for Washington, Jefferson, Monroe, and others, that there will be specific, concrete harm to someone or some ongoing matter if the information sought were disclosed. The privilege protects against generalized institutional harm to important public interests.

Both forms of executive privilege are theoretically relevant in the debate over Bolton’s testimony. As Trump has suggested, Bolton knows details about diplomatic relationships and national security interests that, if disclosed, could inflict damage to those ongoing concerns. But Bolton also has knowledge about internal deliberations and communications with the president, the disclosure of which would cause harm only to the undifferentiated confidentiality interests in such communications.

That distinction—between concrete and generalized harms—has been largely absent from the discussion of executive privilege and Bolton’s testimony. But it is crucial to understanding what it means to protect the presidency or protect executive privilege when discussing his potential testimony.

During Watergate, Richard Nixon claimed that the undifferentiated confidentiality interests underlying executive privilege provided him an absolute privilege to withhold information from Congress and the courts when he, and he alone, decided it was necessary. But the Supreme Court rejected that view of privilege in U.S. v. Nixon: “The President's need for complete candor and objectivity from advisers calls for great deference from the courts. However, when the privilege depends solely on the broad, undifferentiated claim of public interest in the confidentiality of such conversations, a confrontation with other values arises” (emphasis added).

Both concrete and undifferentiated interests can be the basis for a claim of executive privilege. Nixon holds that, when the interests in question represent generalized confidentiality concerns, they must yield when another branch has a constitutional need for specific, concrete information. In the Nixon case, the “confrontation with other values” occurred with respect to the judiciary. And in addressing how that confrontation should be resolved, the Supreme Court repeatedly distinguished between general and specific harms:

A President's acknowledged need for confidentiality in the communications of his office is general in nature, whereas the constitutional need for production of relevant evidence in a criminal proceeding is specific and central to the fair adjudication of a particular criminal case in the administration of justice. Without access to specific facts a criminal prosecution may be totally frustrated. The President's broad interest in confidentiality of communications will not be vitiated by disclosure of a limited number of conversations preliminarily shown to have some bearing on the pending criminal cases. [emphasis added].

On several occasions, the Supreme Court in Nixon also took pains to note that the president had not claimed that the disclosure of the information sought would cause damage to the national security or diplomatic relations, and the court recognized that the judiciary has often deferred to presidents’ determination about that type of specific, concrete damage.

Bolton appears willing to testify about the president’s understanding of the withheld aid to Ukraine and the actions of Rudy Guiliani and his associates, and I have not seen anyone argue that the disclosure of that specific information would cause concrete, identifiable harm to the national security or a current diplomatic relationship. Instead, the defenders of executive privilege have cited generalized confidentiality interests and the need to protect the “presidency” against the damage that would occur if the Senate sought testimony from the president’s former national security adviser.

That argument—that the Senate should decline to seek specific evidence relevant to impeachment in order to protect the presidency’s generalized institutional interests—badly distorts executive privilege and ignores its fundamental purpose. The doctrine itself provides the necessary protection for the presidency by establishing a presumptive privilege for various categories or components of confidential executive branch information. As established by the Supreme Court and practiced by the executive branch, executive privilege protects against both concrete, specific harm from disclosure and undifferentiated harm to generalized confidentiality interests. But the protection it provides varies with respect to those different interests. Undifferentiated claims of public interest in maintaining confidentiality give rise to a presumptive privilege only. And when confronted with “the constitutional need for production of relevant evidence” that is “specific and central” to the fulfillment of another branch’s constitutional duty, those generalized interests are overcome by the other branches’ specific interests.

The information contained in Bolton’s book is likely no different in kind from many “tell-all” books written by former presidential advisers, which often relate private conversations and deliberations among the president and his staff to which only a handful of people had access. Some even include purported direct quotations of the president’s words. That’s why the books sell; they include information that is not otherwise available, a rare window into the Oval Office.

Could the publication of this type of book harm the presidency’s or the executive branch’s generalized confidentiality interest? Perhaps. But the First Amendment allows these individuals to speak, consistent with their obligations to refrain from disclosing classified information. The Constitution establishes that the interests served by the freedom of speech should be elevated over other public interests if a conflict arises.

The Constitution, of course, does not mention executive privilege; it is an authority inferred from the structure of the Constitution and separation of powers. But it does explicitly provide for impeachment by the House and trial by the Senate. And it gives Congress that solemn responsibility, the sole authority to consider impeachment and removal from office.

Nixon recognized that, in a criminal trial, “[t]he need to develop all relevant facts in the adversary system is both fundamental and comprehensive.” The Senate is not a criminal court, and it alone determines whether it wants to develop all relevant facts or not for an impeachment trial, an inherently political trial. But if the Senate determines that specific evidence is necessary to perform its constitutional function, executive privilege based on a generalized interest in confidentiality cannot bar that evidence. The Senate’s specific constitutional need prevails over an undifferentiated need for confidentiality.

Senators’ refusal to request the evidence does not protect executive privilege. And attempting to withhold the information does not protect the presidency. A Senate subpoena for specific, relevant information in an ongoing impeachment trial would not inhibit any president from asserting or relying on executive privilege in the future, and it certainly would not prevent a president—including this one—from raising privilege on the basis of specific, identifiable harms that disclosure of particular information could create. Assertions by both the White House and its Republican allies that the Senate should or must refrain from seeking evidence directly relevant to an ongoing impeachment trial because of a potential claim of executive privilege do nothing other than diminish the Senate’s authority going forward. Those assertions elevate undifferentiated claims of executive branch confidentiality interests above the Senate’s solemn constitutional duty to consider whether to remove the president from office.

If the Senate does not want to hear from Bolton, that is its choice—and a valid exercise of its constitutional prerogative to try impeachments. But it should not attempt to justify that action by a need to “protect” executive privilege or the presidency.