Now that the House of Representatives has impeached President Donald J. Trump for alleged high crimes and misdemeanors, proceedings will shift to the Senate, which has the “sole Power to try all Impeachments” under Article I, Section 3 of the Constitution. That provision establishes certain basic rules for impeachment trials—the Senate shall be on “Oath or Affirmation;” the Chief Justice presides since the President is the defendant; conviction requires a two-thirds vote and can impose no punishment except removal from office and disqualification from future office—but leaves much to the imagination. So what else can we deduce about the nature of Senate impeachment trials under the Constitution? Quite a lot, as it happens.
The first and most important point about all matters of procedure for Senate impeachment trials is that they are utterly immune from judicial review. In Nixon v. United States (1993)—a case involving not President Richard Nixon but Judge Walter Nixon—the Supreme Court held that challenges to impeachment procedures present a “political question” that cannot be resolved by courts. This flows from the Senate’s “sole Power” to try impeachments, as well as the more general power of each House of Congress to “determine the Rules of its Proceedings.” Nixon concerned a Senate rule permitting a committee of twelve Senators, rather than the whole Senate, to hear evidence in an impeachment trial and submit a report to the full Senate, but its reasoning would apply to any procedural dispute within an impeachment trial.
This does not mean that the Constitution places no restraints on the trial of impeachments. Indeed, there is a strong case that the specific procedure at issue in Nixon is unconstitutional! But the responsibility for ensuring that Senate impeachment practice conforms with the Constitution falls solely upon the Senate itself, just as it has final, unreviewable authority to determine the meaning of “high Crimes and Misdemeanors.” The only constitutional remedy for procedural mischief by the Senate must be political.
How, then, should the Senate understand its role in trying impeachments, and what the trial should look like? The strongest clue we have, by far, as to the appropriate nature of impeachment proceedings in the Senate is the use of the word “try.” Although they are not spelled out in the text, this is a word rich with implications. A trial is a proceeding to test a cause, in this case, the allegations against the President. In our legal tradition, stretching back to the English common law, trials are generally adversarial, with each side introducing evidence, advocating their position, and challenging the other side’s contentions. The Constitution does not specify who plays these adversarial roles in an impeachment trial, but the general practice—the House of Representatives acting as the prosecution, represented by its “impeachment managers,” and the impeached President as the defendant, represented by counsel—accords with common sense.
There are two other important roles in a trial in the Anglo-American legal tradition: the judge and the jury. Actually, these are three roles disguised as two: a trial judge serves as both the presiding officer, ruling on questions of evidence and procedure, and as the “judge of the law.” The jury, meanwhile, acts as the “judge of the facts.” What this means is that the judge will give “instructions” to the jury explaining the relevant legal standards they must apply, and in theory, at least the jury’s only function is to determine whether, as a factual matter according to the evidence, those standards have been met.
In an impeachment trial, the Senate itself serves in all three of these capacities, broadly speaking. The Chief Justice is formally the presiding officer and exercises those functions of a trial judge, but the Senate may always overrule his decisions by a majority vote. And it is firmly settled at this point that the Senate judges both the facts and the law when it renders its final judgment of conviction or acquittal. During President Bill Clinton’s trial in 1999, Senator Tom Harkin objected to the House managers’ repeated reference to Senators as “jurors,” which he believed improperly implied that they could only judge the facts of the case, and Chief Justice William Rehnquist agreed.
Because the Senators are judges as well as jurors, there will be no “jury instructions” from Chief Justice Roberts or anyone else. Instead, each side will make arguments not only about what facts the evidence has established, but whether those facts amount to “high Crimes and Misdemeanors” under Article II, Section 4. And the Senate’s verdict will reflect both its factual conclusions and its legal judgment. The Senate is in no way bound by the House’s assertion that President Trump’s conduct rises to the level of an impeachable offense. This may be particularly significant as to the second article of impeachment, whose factual allegations—that the President has resisted House subpoenas and requests for documents and testimony—can not really be controverted. If the Senate acquits on that charge, it will presumably be because it does not consider that conduct impeachable, and that is its call to make.
Under the adversarial system, the Senate’s role in the development of that evidence is passive. That means the responsibility of introducing evidence falls on the parties themselves, and the House of Representatives may be understood to have the burden of production (so if neither party introduces any evidence then the Senate must acquit). The Constitution does not specify rules of evidence, and as Hilary Hurd and Benjamin Wittes of Lawfare recently wrote, neither do the Senate rules for impeachment trials. A 1999 report from the Congressional Research Service suggested that the committee that has tried many judicial impeachments has tended to follow something like the Federal Rules of Evidence, which are quite restrictive, for example excluding “hearsay” statements.
Constitutional considerations, however, would point in the other direction: The Senate should feel itself free to consider any evidence that might be relevant or informative. As noted, the Senators cannot actually be sequestered from the kinds of extraneous information that an ordinary jury would be shielded from. And if we are already trusting Senators to set aside whatever they may have heard about the President’s conduct outside the trial, it stands to reason that we should also trust them to appropriately discount evidence introduced at trial that is of dubious reliability.
Although the Senate is of course not required to receive evidence it does not think would be helpful, in the spirit of fairness and in light of the monumental national stakes it should err in favor of allowing each side an opportunity to present its case in full. The rules limiting the introduction of irrelevant evidence in an ordinary trial are designed to prevent the jury from being unduly influenced by those materials and to avoid wasting time. Neither concern is relevant here. Again, the entire premise of the trial is that we can trust Senators to sort these things through, and when the question is the fate of a Presidency the danger of wasting a little time is minimal compared to the paramount interest in a complete airing of anything that might possibly bear on the decision. But at the end of the day, it is the Senate's prerogative to decide how much or how little evidence it wants to hear.
After the New Year, Part II will explore deeper questions such as the burden of proof, the requirement of neutrality, and how each of the different actors during the trial should understand their role and their obligations.
Robert Black is Senior Fellow for Constitutional Content at the National Constitution Center.
Resources from the Interactive Constitution
The House's Impeachment Powers
