Now that the Democrats have won control of the House of Representatives, there will be a flood of congressional investigations of waste, fraud, and abuse within the Trump administration, as well as a number of investigations that bear directly on the Trump campaign and President Donald Trump’s conflicts of interest. As the gavels switch hands to President Trump’s political opponents, a colleague asked me, can an investigating committee subpoena President Trump to testify at a congressional hearing?

At first blush, it sounded preposterous to my ears — having been trained in Congress and the White House Counsel’s Office during the oversight battles of the Clinton, Bush, and Obama eras. But it is a legitimate question that raises complicated issues of constitutional law, institutional power, and political leverage. A number of historical episodes and court cases bear on the answer.

Has Congress ever subpoenaed a president to testify in an oversight investigation?

As best I can tell, Congress has never subpoenaed a sitting president to seek to compel testimony.

However, Congress has subpoenaed a number of former presidents amid investigations touching on their conduct in office — with mixed results.

In 1848, Representative Charles Ingersoll (D-Pa.), who chaired the House Committee on Foreign Affairs, accused Secretary of State Daniel Webster of misusing funds related to a secret “contingent fund” used by presidents for clandestine intelligence operations. Disbursements from the fund at issue required presidential signatures, which led Congress to seek the testimony of former Presidents John Tyler and John Quincy Adams. In office at the time, President James Polk refused to provide detailed information to Congress as a matter of comity to the prior administrations. Thereafter, Congress subpoenaed the two former presidents. Two select investigative committees questioned Tyler, and Adams provided a sworn deposition to one of them.

In contrast, Congress failed in an attempt to compel testimony from former President Harry Truman during the Red Scare and McCarthy era. On November 10, 1953, the House Committee on Un-American Activities (HUAC) subpoenaed not a sitting president, but former President Harry Truman (along with his former attorney general and then-Supreme Court Justice Tom Clark and his former Secretary of State and then-Governor of South Carolina James Byrnes) to testify about the circumstances of Truman’s appointment of an Assistant Secretary of Treasury who had come under suspicion of Communist ties. (There are conflicting accounts as to whether that subpoena was issued by Chairman Harold Velde (R-Ill.) unilaterally or by the Republican committee majority).

Truman sent a letter to the committee on November 12 refusing to honor the subpoena on separation of powers grounds. Four days later, he went on national television and radio to explain himself and denounce Eisenhower’s Attorney General for dishonesty and embracing McCarthyism. Truman’s public defense would undermine an executive privilege claim of confidentiality, but HUAC never tested Truman’s legal theory because it did not seek to enforce its subpoena by a finding of contempt. (For a brief recitation of Congress’s contempt power, see this article related to Steve Bannon’s congressional appearances.)

Even once out of office, congressional efforts to compel testimony from former presidents raise many of the same constitutional and institutional issues as disputes with sitting presidents. While the executive branch confidentiality interests in information held by former presidents may be somewhat attenuated due to the passage of time, their presidential secrets may still have current salience (e.g., a secret arising during a prior presidency that could damage current relations with a foreign power) or revelations of which could damage the executive branch as an institution (e.g., a highly sensitive internal deliberation in a prior administration that, if disclosed now, could chill and hamper similar deliberations in the future).

On the other hand, time will often weaken the need for confidentiality. In addition, the current president largely has ultimate control of the records of the prior administrations. Principles of comity guide the relations between presidents, but they may not result in the realization of a prior president’s wishes. For example, President Barack Obama might not treat post-9/11 records of rendition, detention, and interrogation sought by Congress in the same manner that President George W. Bush would have.

The precedent here demonstrates that Congress has overcome the executive branch objections and successfully compelled information from two former presidents for information related to their tenure in office.

Have presidents ever testified under oath before Congress?

Yes, but exceedingly rarely and only as a voluntary matter.

A number of former presidents and vice presidents have testified in Congress, as has at least one sitting vice president. But three sitting presidents — George Washington, Abraham Lincoln, and Gerald Ford — have testified before Congress. Another — Woodrow Wilson — submitted to hours of committee questioning at the White House. All of them did so voluntarily rather than under legal compulsion.

When such testimony has occurred, it has typically been to further a policy goal championed by the White House principal. For example, Wilson invited the Senate Foreign Relations Committee to convene at the White House in order to promote the League of Nations and passage of the Treaty of Versailles. Tantamount to a field hearing, Wilson read a prepared statement to the committee members and then submitted to over three hours of questioning. Nonetheless, the Senate failed to ratify the treaty.

Sometimes that policy goal arises in the context of a congressional investigation. For example, two years after Theodore Roosevelt left the White House, he testified before a special investigative committee in the House that was tasked with investigating United States Steel Corp. As a famous “trust buster,” he was in favor of breaking up Big Steel, so testimony before that committee in that context helped further Roosevelt’s policy goals.

President George Washington testified before the entire Senate on August 22, 1789 on the subject of Indian treaties. He appeared seeking Senate advice under its Article II “advice and consent” role in treaty making. It proved to be a parliamentary procedure disaster, and “no President of the United States has since that day ever darkened the doors of the Senate for the purpose of personal consultation with it concerning the advisability of a desired negotiation.” (Corwin, p. 210).

But, as sitting presidents, Lincoln and Ford testified before investigating committees amid national controversy. As a formal legal matter, both appeared voluntarily rather than under the compulsion of a subpoena. However, public political pressure certainly affected their decisions to testify. It is unclear from the record I could find whether they were threatened with subpoenas such that they made their appearances under some threat of legal action.

Have presidents ever given testimonial evidence to congressional investigations short of formal testimony?

Yes, but again rarely and, when it happens the logistics have typically been negotiated so as to avoid the impression that the president or vice president is submitting to the coercive power of the legislative branch.

Sometimes Congress establishes a commission to study a particular topic or investigate a particular incident. To the extent those commissions are exercising legislative inquiry powers delegated by Congress, they are Article I entities for purposes of separation of powers analysis. Put another way, as a matter of constitutional law such commissions are deemed congressional rather than executive or judicial.

For example, the National Commission on Terrorist Attacks Upon the United States — commonly called the 9/11 Commission — was a bipartisan commission created by Congress, by means of legislation that President George W. Bush signed into law, in order to give a full accounting of those horrific attacks. The President appointed its Chairman, while the Democratic leaders of the House and Senate appointed its Vice Chairman. Despite that hybrid method of appointment, Section 601 made it clear the Commission was “established in the legislative branch.” Congress granted it subpoena authority, which it ended up using on three occasions against the Federal Aviation Administration, the Department of Defense, and the City of New York before it negotiated information access to the commissioners’ satisfaction.

There was intense political pressure for President Bush and Vice President Richard B. Cheney to give evidence. They ultimately provided interviews to the 9/11 commissioners. However, they did so neither under oath nor before a formal transcription service. No subpoena issued, but subpoena power was part of the political environment that brought them to the commission. Like plea agreements and presidential vetoes, subpoena authority often does more work in its shadow that when exercised. As one commentator noted, “[t]he in terrorem effect of those subpoenas and the specter of additional subpoenas turned out to be an important lever for getting documents and testimony.”

Has Congress ever subpoenaed a president for documents?

Yes. Since Watergate, several congressional subpoenas seeking documents have been at the heart of some of the greatest confrontations between Congress and the White House.

Most famously, the Senate Select Committee on Presidential Activities subpoenaed President Richard Nixon for the Watergate tapes and other records on at least two occasions. In Senate Select Committee v. Nixon, in May 1974, the D.C. Circuit rejected the Senate investigative committee’s request for a declaration that President Nixon comply with its subpoena to produce the Watergate tapes. In contrast, in United States v. Nixon, in July 1974, the Supreme Court ordered production of the Watergate tapes to a grand jury.

These cases did not definitively establish that a grand jury subpoena in a criminal proceeding per se receives greater weight than a congressional subpoena when courts evaluate competing executive and investigative interests, but they should give Congress some pause. In Senate Select Committee, the D.C. Circuit grounded its decision, in part, in the fact that the House Judiciary Committee had already obtained the tapes. The House (not the Senate) has a constitutional mandate to consider impeachment charges, whereas the Senate sits as a trial chamber related to the evidence gathered by the House. Therefore, there is reason to believe the court might have been more solicitous of the House’s need for the tapes than the Senate’s.

Have presidents ever been subpoenaed to testify in judicial or other adjudicative proceedings?

Yes. While it raises separations of powers sensitivities, sitting presidents and vice presidents have received subpoenas, and thereafter testified, in both criminal and civil proceedings. In 1818 President James Monroe was subpoenaed to testify in a court martial against a naval officer, and while conceding jurisdiction of the subpoena he negotiated written interrogatories to avoid having to leave the seat of government. In criminal cases, presidents have testified both as third-party witnesses (e.g., Ronald Reagan’s deposition in the Iran-Contra criminal trial of his former national security adviser Rear Adm. John M. Poindexter) and subjects under investigation (e.g., Bill Clinton’s testimony as a grand jury witness in the Whitewater independent counsel investigation). Many observers believe that the Supreme Court’s ruling in United States v. Nixon would extend beyond documents to presidential testimony because of its stark language about grand jury’s need for evidence – as well as the overwhelming strength of public interest – in criminal cases.

In civil trials, presidents and vice presidents have testified as witnesses and as defendants. In Clinton v. Jones, the Supreme Court rejected Clinton’s argument that the demands of the presidency rendered him immune—at least during his term in office—from compelled participation in civil litigation. Clinton had argued the president “occupies a unique office with powers and responsibilities so vast and important that the public interest demands that he devote his undivided time and attention to his public duties.” After finding immunity did not apply, the court suggested the court should manage the proceedings such “that interference with the President’s duties would not occur.” Thereafter, Clinton participated in civil deposition as a defendant in Paula Jones’s sexual harassment suit before ultimately settling the case out of court.

However, while the testimony of a president happens, it happens very rarely when compared to the number of litigants and investigators who seek presidential testimony. As they should, courts tend to temper their power to compel evidence with the demands of the presidency as well as comity between the judicial and executive branches. There are limits, though, to judicial accommodation of the president. For example, the court overseeing the criminal trial after Lynette (Squeaky) Fromme’s attempted assassination of President Gerald Ford rejected Ford’s request for written submissions, requiring instead that he submit to a videotaped deposition. (The defendant’s cross-examination rights undoubtedly played into that ruling.) Moreover, notwithstanding the Supreme Court’s admonitions in Jones about deferential trial management, it was that civil discovery that set forth the chain of legal events that led to Clinton’s impeachment.

What about controversies in which the president did not testify before congressional investigating committees?

As one contemplates the limited historical evidence of presidential testimonial participation in congressional investigations, that precedent needs to be weighed against significant instances of non-participation.

Atop this category sits impeachment proceedings. As set forth in the Constitution, the House may impeach a president, vice president, judge, or other civil officer of the United States, for “treason, bribery, or other high crimes and misdemeanors” by a majority vote. Impeachment by the House is somewhat akin to a charging document like an indictment, and the Senate conducts the trial and sits in judgment on guilt and removal from office. Two presidents — Andrew Johnson and Bill Clinton — have been impeached by the U.S. House of Representatives, but then avoided removal by the Senate. Neither Johnson nor Clinton testified at their own Senate impeachment trials.

By historical accounts, Johnson wanted to testify on his own behalf but his lawyers convinced him it would be inflammatory and counterproductive. I found no evidence the House managers sought to include Johnson among their 25 witnesses, which could have created its own constitutional confrontation as well as implicating President Johnson’s Fifth Amendment right against self-incrimination.

In addition, Nixon — like Johnson and Clinton — did not testify before the House Judiciary Committee as it conducted its impeachment inquiry. While Reagan gave evidence in the Iran-Contra criminal trials, he was not a witness in the congressional Iran-Contra hearings.

The case for a congressional subpoena of President Trump

Congress always needs information in order to formulate policy and provide resources to protect American electoral integrity. Congress also has a constitutionally based mandate to investigate executive branch maladministration and abuse.

Congress’s investigative need in the Trump era is even greater than normal. Russia undertook active measures to subvert U.S. democratic elections, and President Trump is suspected of obstructing the resulting criminal and counterintelligence investigations. Moreover, President Trump’s refusal to divest from his personal business interests raise a host of conflict-of-interest issues that call for oversight. While a lot of preliminary investigative work would need to be done before the time would be ripe for presidential testimony, many of the pressing oversight issues relate to the personal and official conduct of Donald Trump himself.

The historical precedent for presidential testimony makes it clear that the president is not immune from legal process. While a congressional subpoena for presidential testimony raises significant separation of powers sensitivities, it is not unthinkable that Congress could have an acute enough need for the president’s personal testimony that is would support a subpoena. The big ticket executive privilege cases — United States v. Nixon, Senate Select Committee v. Nixon, House Judiciary Committee v. Miers, and House Oversight Committee v. Holder/Lynch — all require balancing congressional or grand jury investigative needs against the president’s confidentiality interests. I do not see executive branch confidentiality interests outweighing Congress’s as a categorical legal matter.

The case against a congressional subpoena of President Trump

While investigative need for evidence from President Trump is high and the legal case for a subpoena is colorable, practical and institutional considerations militate against that kind of interbranch brinksmanship. A congressional subpoena seeking to command President Trump’s appearance before an investigating committee would be unprecedented and highly provocative — playing with fire in a tinderbox political environment.

Enforcing compliance of such a subpoena would be exceedingly difficult. As the House Judiciary Committee noted when considering issuing subpoenas for records to President Nixon:

Realistically, the President probably cannot be compelled to Comply with a subpoena duces tecum by use of the processes of either the House or the courts. Rather than being considered solely in terms of the availability of coercive means of enforcement, however, noncompliance may also be addressed in terms of its effect in the impeachment proceeding itself. This question is one of first impression. There is no direct precedent, and what little material exists from past impeachment inquiries is of limited usefulness.

That analysis was written before the Supreme Court had ruled in United States v. Nixon, but it was also written prior to the D.C. Circuit’s disparate treatment of Senate subpoena authority in Senate Select Committee v. Nixon.

In terms of judicial resolution, there are additional reasons to be highly skeptical that the Supreme Court would rule to enforce a congressional subpoena commanding presidential testimony before Congress. Notwithstanding the historical episodes related to congressional appearances by senior White House advisers, former White House occupants, and sitting presidents, Congress has never successfully compelled a president to testify by means of a subpoena. What’s more, testimony is not the same as document production. A court may treat live testimony as more disruptive of the separation of powers and more burdensome to the presidency than the production of documents.

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In the final analysis, the House could issue a subpoena seeking the president’s testimony in an investigation. Even if that subpoena were legally sound and warranted by the investigative facts, congressional leaders would need to take into account the institutional damage that could come from an unenforced command.

Image of a Senate subpoena of President Richard Nixon for tapes of Oval Office recordings during the Watergate investigation.