Washington(CNN) Chief Justice John Roberts, who is presiding over the impeachment trial of President Donald Trump, scolded both the Democratic House managers and the President's defense team early Wednesday morning after a contentious exchange on the Senate floor.
The extraordinary moment capped an acrimonious opening to Trump's impeachment trial, and placed Roberts, who otherwise largely handled procedural tasks on day 1, in the position of reminding advocates for both sides to maintain decorum during a highly partisan affair.
"I think it is appropriate for me to admonish both the House managers and the President's counsel in equal terms to remember that they are addressing the world's greatest deliberative body," Roberts said. "One reason it has earned that title is because its members avoid speaking in a manner and using language that is not conducive to civil discourse."
Roberts had just listened to the impeachment managers and Trump's legal team rip into each other after House Judiciary Chairman Jerry Nadler made the case for issuing a subpoena for former national security adviser John Bolton's testimony.
During that argument, Nadler accused Republican senators of "voting for a coverup" by killing amendments for documents and testimony of additional witnesses.
"So far, I'm sad to say, I see a lot of senators voting for a coverup. Voting to deny witnesses and obviously a treacherous vote," Nadler said. "A vote against an honest consideration of the evidence against the President. A vote against an honest trial. A vote against the United States."
That led to White House counsel Pat Cipollone firing back during his own remarks: "The only one who should be embarrassed, Mr. Nadler, is you. For the way you addressed this body. This is the United States Senate. You're not in charge here."
Roberts said that kind of exchange was not appropriate and, providing a historical example, reminded the legal teams they they need to be on their best behavior.
"In the 1905 Swayne trial, a senator objected when one of the managers used the word 'pettifogging' and the presiding officer said the word ought not to have been used," Roberts said. "I don't think we need to aspire to that high of a standard, but I do think those addressing the Senate should remember where they are."
Throughout Tuesday's trial, Senate Republicans defeated a series of amendments from Senate Minority Leader Chuck Schumer to subpoena the Trump administration for Ukraine documents as well as testimony from key administration officials. The Senate ultimately killed those amendments and approved rules for the trial on a party-line vote without addressing whether the chamber should subpoena documents or witnesses.
In his role as chief justice, Roberts presides over the trial -- his constitutional duty -- in a role that is highly public but unlikely to see him cast any votes. He has recited procedural rules, kept the clock and read aloud vote tallies.
Heading into the Senate trial, Roberts likely anticipated all manner of possible disruption, by senators, the House managers and perhaps even Trump, with whom he has tangled in the past.
The chief justice has long been known for his extensive preparation and an ability to foresee what's ahead that some colleagues have likened to three-dimensional chess.
CORRECTION: This story has been updated to correct Judge Charles Swayne's name.