Chief Justice of the Supreme Court John Roberts will be sworn in on Thursday at 2 p.m. to preside over the impeachment trial of President Donald Trump. Many are asking what will Roberts do, and some have even suggested that Roberts may descend on the Senate like some kind of Due Process vigilante.

Realistically, Roberts’s ability to accomplish anything of consequence during the Trump impeachment trial is meager at best. That’s no knock to Roberts as an individual, it’s just how impeachments work. Let’s look back at what happened when last we impeached our president.

Then-Chief Justice William Rehnquist presided over the impeachment trial of Bill Clinton. Later, Rehnquist famously wrote, “when asked what I did at the trial I took a leaf out of [the Gilbert and Sullivan comic opera] Iolanthe and replied, ‘I did nothing in particular, and did it very well.'”

Adorably self-deprecating as that anecdote sounds, it’s also fairly accurate. During the entire impeachment trial, Rehnquist made only one ruling that even approached substantive law: he instructed those prosecuting the impeachment to “refrain from referring to the Senators as jurors.” Not exactly a bombshell ruling, as it amounted only to a semantic direction for those arguing Clinton’s case.

One reason Rehnquist did so little is that no one even asked him for rulings. The evidence introduced at the trial had all been agreed upon by stipulation between Democrats and Republicans before proceedings began. The broader reason for Rehnquist’s (and almost certainly, Roberts’s) hands-off involvement is a direct function of constitutional rules on impeachment. Although the Chief Justice of the Supreme Court “presides” over presidential impeachment trials, not much authority is packed into that position.

Being the “presiding officer” of a presidential impeachment trial is not the same thing as being the judge in a typical courtroom trial. Normally, in any fact-finding proceeding that uses a jury, a judge’s role is two-fold: 1) to answer questions of law; and 2) maintain the procedures and rules of the courtroom itself. At an impeachment trial, however, both such responsibilities belong to the Senate. The Senate itself has the authority to decide what its own rules will be, to enforce those rules, and to raise and settle any legal questions that arise during or about the proceedings. As was the case for Rehnquist, Roberts’s power is only as strong as its limitation.

The Senate rules say that they give the “presiding officer” some power, such as the authority to issue “orders, mandates, writs, and precepts” (Rule V), to “direct all the forms of proceedings while the Senate is sitting for the purpose of trying and impeachment” (Rule VII), and to “rule on all questions of evidence including, but not limited to, questions of relevancy, materiality, and redundancy of evidence” (Rule VII). At Trump’s trial, Roberts’s authority is limited by the general will of the Senate. If he makes a ruling, that ruling can be questioned by any senator – and then overruled by a simple majority vote.

As compared with the Clinton trial, there’s less that’s been settled in advance of Trump’s trial. Theoretically, that could mean that more questions are submitted to Roberts. But any ruling he issues would be reviewable by the Senate itself. If the Senate doesn’t like Roberts’s ruling, it could simply vote otherwise. And unlike an ordinary trial, there’d be no venue for the losing side to direct an appeal.

Such a setup should seem pretty quirky for anyone familiar with due process. This would be like a criminal defense lawyer raising an evidentiary objection, the trial judge ruling to sustain that objection, and then the jury outvoting the judge on the basis that it simply really wants to hear what the testimony would have been. Odd for a legal proceeding – but impeachment is not a legal proceeding. It is a political proceeding.

Let’s remember, too, that when the highest judge in the land presides, it’s the exception and not the rule. In non-presidential impeachments, the Vice President of the United States usually presides over Senate trials. Chief Justice Roberts isn’t presiding because the Trump impeachment trial requires his unparalleled courtroom expertise. He’s simply standing in for Mike Pence, who would have an obvious conflict-of-interest in a case potentially culminating in the president’s removal from office. Whether Roberts or Pence is the presiding officer though, the impeachment trial is a Senate proceeding. The Senate has a set of standing rules that govern impeachment trials, and they’re the same whether it’s the chief justice or someone else presiding.

Apart from impotent procedural rulings on issues that may never get raised, is there any other role of consequence for Roberts?Constitutional scholar Frank Bowman, the Floyd R. Gibson Missouri Endowed Professor of Law at University of Missouri Law School, wrote on SCOTUSblog that there might be an additional role for Roberts as tiebreaker. Bowman explained that if there were a procedural issue on which Roberts had not yet ruled, and the Senate were evenly divided as to how to proceed, Roberts’s vote could control:

This result flows from the fact that the chief justice, when acting as presiding officer, is not a judge, but instead assumes the role otherwise played by the vice president in nonpresidential impeachments. Article I, Section 3 of the Constitution says: “The Vice President of the United States shall be President of the Senate, but shall have no Vote, unless they be equally divided.” It is not absolutely certain that this provision extends to impeachment proceedings, but I would hard-pressed to formulate a contrary argument. And we know that Chase did break a procedural tie during the Johnson impeachment, and his exertion of authority was upheld by the Senate.

As a judge, Roberts isn’t likely to relish any power that’s heaped his way. In typical trials, there are statutory rules of evidence and procedure that the judge is (at least theoretically) enforcing as the guidelines for the proceedings. There’s nothing parallel for impeachment trials. There’s no statute or rule book to which Roberts could point as the basis for any particular ruling. Rather, the Senate’s rules are what the Senate says they are. Roberts (as most appellate judges) would be reluctant to take any action approaching “creating law” on a normal day. To do so in the most politically-charged proceeding of our day–examining the actions of a president who has publicly tousled with Roberts over the neutrality of judges generally–likely isn’t the chief justice’s style.

[Image via Jim Lo Scalzo – Pool/Getty Images]

This is an opinion piece. The views expressed in this article are those of just the author.