Caroline Fredrickson is former president of the American Constitution Society and author of “The Democracy Fix: How to Win the Fight for Fair Rules, Fair Courts, and Fair Elections.”

As he presides over the impeachment trial of President Trump, Chief Justice John G. Roberts Jr. does not need to act like a potted plant — nor should he. In fact, Roberts as presiding officer has the ability to force senators to be true to their oath to “do impartial justice according to the Constitution and laws.”

Under the Senate’s standing rules, the presiding officer has the power to issue “orders, mandates, writs, and precepts,” to “direct all the forms of proceedings while the Senate is sitting for the purpose of trying and impeachment” and to “rule on all questions of evidence including, but not limited to, questions of relevancy, materiality, and redundancy of evidence.” To emphasize the limits of Roberts’s role, some commentators argue that these seemingly broad powers are actually quite constrained, because the Senate majority retains the power to overrule Roberts.

But that does not make the chief justice’s role a nullity. Certainly, were Roberts to rule to admit evidence at the request of the House managers, a Republican senator could object and request a vote. With their majority in the Senate, the Republicans could easily prevail and have evidence excluded. Because the Senate has the final word in impeachment, the House managers have no ability to appeal — at least not to a higher court. But imagine how such a move would influence the proceeding. Would Republican senators really want to demonstrate such unprecedented partisanship, overruling the conservative, Republican-appointed chief justice and lending credence to assertions that they are running a rigged trial and burying relevant evidence?

Roberts has attempted, at times, to position the administration of justice and the role of the judiciary as being above the fray of partisan politics. That desire argues for a more assertive role from the chief justice at the impeachment trial, not less. Now more than ever, Roberts must live up to his own vision of dispensing justice by ruling to admit evidence that will advance the goal of seeking the truth.

In doing so, he would be playing a familiar and impartial role one for which he is well suited. During ordinary court proceedings, judges determine whether evidence is admissible based on whether it is relevant and important to the consideration of the legal issues; they determine whether evidence should be excluded because, for example, it is privileged or unduly prejudicial.

The chief justice as presiding officer should follow such standards in determining how to rule on any demands to admit evidence, allow witnesses to testify or obtain documents. To take one potential example, the president has said he would seek to assert executive privilege to prevent former national security adviser John Bolton from testifying, “for the sake of the office.” The chief justice would seemingly be well situated to determine in the first instance whether and how executive privilege applies in the setting of an impeachment trial.

It would be interesting to see how Republican senators would respond to a ruling by the chief justice that they consider adverse to the president’s interests. Senate Majority Leader Mitch McConnell (R-Ky.) has shown no compunction about stating that he does not want witnesses to testify, a stance at odds with his argument in the 1999 impeachment trial of President Bill Clinton. “It’s not unusual to have a witness in a trial. It’s certainly not unusual to have a witness in an impeachment trial,” McConnell said then, calling a request for three witnesses a “modest” number. Indeed, there has never been an impeachment trial that reached a verdict — for a president or a lesser officer — without witnesses.

But for other Republican senators, especially those facing difficult reelection campaigns, voting to overturn a decision by the chief justice might be a daunting prospect — and rightfully so. As Republican former representative Thomas Campbell, who sat on the House Judiciary Committee during the Clinton impeachment, put it in the New York Times, “How would a senator feel about overruling a judgment on the merits by the chief justice? I think ‘hesitant’ would be the adjective I’d use.”

Those of us who believe the Constitution requires a fair trial — that the Senate oath to uphold “impartial justice” is not meaningless verbiage — must hope that “hesitant” will not be the word historians will use to describe how the chief justice performed his role. Doing little would be ducking his constitutional responsibility, not fulfilling it.

Read more: