Chief Justice to Enter Spotlight…

In contrast with congressional proceedings, Supreme Court arguments aren’t televised, in part to cool the rhetoric and diminish the chance attorneys’ statements or the justices’ remarks can be turned into soundbites. The last time most Americans could observe the chief justice at any length came at his confirmation hearing in 2005, when he told senators a judge’s job was “to call balls and strikes and not to pitch or bat.”

In the 14 years since President George W. Bush nominated him to succeed the late William Rehnquist, Chief Justice Roberts has strived to portray the judiciary as an institution apart from the political branches of the presidency and Congress. While Republicans and Democrats have fought bitterly over judicial vacancies, he has insisted that the courts are independent of the partisan fray, resolving disputes despite ideological differences.

The nature of impeachment, with legislative bodies employing judicial-type procedures to accuse and decide guilt in alleged political crimes rather than legal infractions, confuses those distinctions.

Chief Justice Roberts, seated during the trial at the Senate chamber’s rostrum, might appear to be the authority before whom the president’s accusers and defenders plead their cases. Yet he will hold less power over the proceedings than a municipal court judge hearing a pickpocketing case. The trial’s rules will be written by the jury—the Senate—whose Republican leadership has already pronounced the defendant not guilty.

The Trump trial procedures will be adapted from the Senate’s 1986 impeachment guidelines, which allow the chief justice to decide “questions of relevancy, materiality, and redundancy of evidence,” among other matters. But the Senate can overrule those decisions by simple majority, akin to letting seven of 12 jurors reverse a trial judge on any given motion in an ordinary case.

There have been 19 impeachment trials since the Constitution was ratified in 1788, but only two involved presidents, requiring the chief justice to officiate.

Presiding over President Andrew Johnson’s trial in 1868, Chief Justice Salmon P. Chase took an assertive role and cast at least two tie-breaking votes. The Senate overruled some of his decisions but rejected efforts by Sen. Charles Sumner of Massachusetts to restrict the chief justice’s powers.

In contrast, Chief Justice Rehnquist did his best to stay out of the fray during President Clinton’s 1999 trial and saw none of his procedural rulings challenged. He may have made his greatest impression with his robe, whose sleeves were decorated with gold stripes inspired by the Lord Chancellor’s costume he saw in a production of Gilbert and Sullivan’s “Iolanthe.”

Because trial procedures reflected Senate rules rather than those of the Supreme Court, “when most issues came up, he huddled with the parliamentarian, the person who actually knew this stuff,” says Frank Bowman, a University of Missouri law professor and author of “High Crimes and Misdemeanors: A History of Impeachment for the Age of Trump.”

Chief Justice Roberts is likely to follow the Rehnquist model, Prof. Bowman says. “I think mostly he’s going to sit up there and be a figurehead, every now and again maybe having to make some rulings on the scope of various arguments,” Prof. Bowman says. “He won’t want to get the institutional integrity of his own branch of government all tangled up with this highly partisan exercise.”

That may not be so easy in the age of social media. Within the Senate chamber and beyond, today’s political climate may exaggerate insubstantial moments and disguise consequential events as the trial unfolds.

President Trump has denigrated judges and courts that issued decisions he found objectionable, a practice that prompted a rare rebuke from Chief Justice Roberts himself last year. And although the president has treated the chief justice with respect during their personal encounters, as a candidate Mr. Trump labeled him “a disgrace” and an “absolute disaster” for his votes upholding portions of the Affordable Care Act.

“If the chief justice rules against the president on a particular issue, there are going to be people who object to what the chief justice has done, no matter how fair or appropriate that ruling might be,” says Kathryn Webb Bradley, a Duke University law professor who worked with Chief Justice Roberts when he was in private practice. “I would expect that it wouldn’t faze the chief justice at all.”

Mr. Martin, of Washington University in St. Louis, agrees.

“I think that the opportunity is there for him to emerge, and thus the court to emerge, from this entire episode as being above the raw politics of the day,” he said. “If the chief can do that, it would be a great thing for the country. And I think it sets the court up to decide some really profound issues, about the separation of powers, about the presidency, that are on their docket.”

While the impeachment trial may be a singular episode for the Senate, it is in many ways an opening act for the Supreme Court. In March, the justices are set to hear Mr. Trump’s arguments to stymie subpoenas issued by House investigators and a state grand jury for his financial records—including the hush-money payments to women who said they conducted extramarital affairs with him. (Mr. Trump has said he didn’t have affairs with them.)

Also, several Trump administration policies, including its plan to cancel an Obama-era reprieve for illegal immigrants brought to the U.S. as children, are pending before the Supreme Court, which is expected to render rulings in June.

Those cases are likely to see the chief justice cast a deciding vote between the court’s ideological wings, rendering his own judgment on matters essential to President Trump.

Write to Jess Bravin at [email protected]