Whatever the precise parameters of his role, Chief Justice Roberts will be front and center if the Senate considers, and ultimately votes upon, allegations that President Trump has committed “high Crimes and Misdemeanors.”

With two cases involving efforts to access President Donald Trump’s tax records already at the U.S. Supreme Court, and more cases involving congressional oversight likely to be there soon, all eyes are on the court that Chief Justice John Roberts leads. And all eyes may be on the chief justice himself soon if, as seems likely, the House’s ongoing impeachment inquiry turns into a Senate impeachment trial. No matter how senators ultimately vote at any trial, the chief justice’s role there could shape the decisions he makes on the court well into the future.

The constitutional rules governing impeachment are sparse, but the broadest guidelines are clear. The president and other civil officers “shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or high Crimes and Misdemeanors.” The U.S. House of Representatives has the “sole Power of Impeachment,” but impeachment alone doesn’t remove someone from office. Instead, a person can be removed from office only if two-thirds of the members of the Senate, which “shall have the sole Power to try all Impeachments,” vote to convict. And ”[w]hen the President of the United States is tried, the Chief Justice shall preside.”

The Constitution doesn’t provide any details about what the chief justice should do as presiding officer over a trial of the president, but the Senate rules governing impeachment provide, among other things, that the “Presiding Officer possesses authority to rule on all evidentiary questions,” or he can “put any such issue to a vote before the Senate.” They also allow that “any Senator may request that a formal vote be taken on a particular question.”

When Chief Justice Salmon Chase presided over President Andrew Johnson’s impeachment trial, he “claimed the authority to decide certain procedural questions on his own, but the Senate … overruled him at least twice.” When Chief Justice William Rehnquist presided over President Clinton’s trial, he “ruled on some procedural questions” that went without challenge by the Senate, but he later diminished the significance of his role, remarking that “I did nothing in particular, and I did it very well.”

Notwithstanding these uncertainties, one thing is clear: Whatever the precise parameters of his role, Chief Justice Roberts will be front and center if the Senate considers, and ultimately votes upon, allegations that President Trump has committed “high Crimes and Misdemeanors.” And he will have literally a front-row seat as the senators hear in detail about this president’s many abuses of the powers of his office.

At the same time that Chief Justice Roberts is playing his constitutionally prescribed role at a Senate impeachment trial, he’ll be continuing his day job as well — and there he may be in the process of deciding one or more of these congressional oversight cases, cases that will surely be political blockbusters and will require two of his colleagues, Justices Neil Gorsuch and Brett Kavanaugh, to decide whether to vote against the president who appointed them to sit on the bench.

For his part, Chief Justice Roberts has long insisted that he and his colleagues are not simply politicians in robes. At his confirmation hearing, he famously likened judges to umpires calling balls and strikes. And although his record leaves no question that he is an incredibly conservative jurist, he has sometimes shown a willingness to part ways with the other conservatives on the court.

But this is a trying time for a justice who wants his court to be seen as an impartial institution. The president has repeatedly suggested that the Supreme Court is in his back pocket — even tweeting that if the “partisan Dems ever tried to impeach, I would first head to the U.S. Supreme Court.” (The Constitution gives the Supreme Court no role to play in the impeachment process.)

These congressional oversight cases will, if the court decides to hear them, be tests of who’s right about whether the court is above politics: Chief Justice Roberts or President Trump. To be clear, these cases shouldn’t be difficult. Congressional oversight has deep roots in our political and legal tradition, and the Supreme Court itself has repeatedly recognized the breadth of Congress’s oversight authority. The president’s arguments against congressional scrutiny would, if accepted, meaningfully cabin Congress’s oversight authority, undermining a fundamental check Congress has long used to hold the executive accountable.

If and when Chief Justice Roberts is asked to preside over an impeachment trial, he will bear witness to a powerful reminder of the critical importance of our nation’s system of checks and balances. That reminder should guide him when he’s doing his day job.