By Nancy Gertner

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It’s common to hear television commentators intone about how an impeachment trial in the Senate is “just” a political process, not a legal one, as if that means a free for all, the typical horse-trading of a legislative session.

While the Constitution is not often specific, when it comes to impeachment, the words are fairly clear, especially on the issues now being debated: Should there be live witnesses at a Senate trial? How impartial should the senators be? Should there be additional evidence in the Senate that was not produced before the House?

Article I, section 3 of the Constitution gives the Senate the “the sole power to try all impeachments.” As noted by the late Charles Black, a leading constitutional law expert who wrote an authoritative book on impeachment, early drafts of the 1787 Constitutional Convention provided for impeachment trials by the Supreme Court; when this was changed to a Senate trial, there was no suggestion that the nature of the proceeding — a trial — would change. “Try” had a specific meaning in the 18th century, not unlike its meaning today — a hearing with live witnesses. “Trial” is defined in Article III, the article outlining the judicial power: “The trial of all crimes, except in Cases of Impeachment, shall be by jury.” The implication is that an impeachment trial is like any other except the decision-maker is the Senate, not a lay jury.

It is no surprise then that when senators “try impeachments,” the Constitution requires an “oath or affirmation” separate from the one they take as senators. The standard oath of office is to support and defend the Constitution. The impeachment oath is to “do impartial justice according to the Constitution and laws,” just like jurors.

Colonial juries at the time of the Constitution’s drafting were different from modern juries, but the differences bring them closer to a Senate impeachment jury. Colonial juries were picked from the rolls of white men with property (women and people of color were not allowed to serve), sadly, not unlike the Senate’s composition. Since the country was largely rural, most trials took place in small towns where prospective jurors knew about the case before it started. Today, we seek jurors who know little about the case before them. Colonial juries were more powerful than modern juries. They were expected to find both the facts and the law, not unlike Senate jurors who can set the impeachment rules. A modern jury is instructed that while they determine the facts, a judge determines what the rules are.

One thing, though, hasn’t changed. Jurors then and now take an oath to be impartial — just like the Senate’s impeachment oath.

Does that mean that Senate Majority Leader Mitch McConnell, who has already announced that he would never vote to remove the president, must be excluded from hearing the case? What about the Democrats who have expressed an opinion about President Trump’s guilt? If we excluded every senator who showed bias, so many would be disqualified that the trial would take place before a relatively small number. That can’t be what the Framers had in mind, according to Charles Black. In fact, the reason why the Framers rejected having impeachment in the Supreme Court, according to Harvard Law Professor Larry Tribe and Georgetown Law Professor Joshua Matz, was not just that they knew the Court could include justices appointed by the sitting president; they reasoned that the Senate’s sheer size as compared to that of the Court would safeguard against corruption.

To the question of whether evidence can be offered in the Senate that was not presented to the House, the answer is, of course. “Impeachment” simply means “accusation” or “charge.” In Federalist No. 66, Alexander Hamilton urged splitting the impeachment process into the accusation and the judging: Think of the House process as similar to a grand jury indicting a suspect and the Senate as the courtroom where the trial takes place. With that split there is no doubt: The Senate can hear evidence the House did not.

However trial-like a Senate impeachment proceeding is supposed to be, there are limits. There is no appeal to the courts, for one. The Senate has “sole power to try all impeachments” under the Constitution. Still, labeling the Senate trial “political” doesn’t mean it is without constitutional direction, stripped of its trial-like nature. The Constitution obliges the chief justice of the Supreme Court to preside, not the vice president as in an ordinary session. And there is that oath. As Black noted, senators were “duty-bound to act on their own view of the law and facts, as free as may be of partisan political motives and pressures.” The question is: Is that possible in 2020?