Supreme Court Chief Justice John Roberts warned the attorneys for President Donald Trump and the House impeachment managers to watch their tone as the first day of the proceedings wound down.

Roberts told both sides to “remember that they are addressing the world’s greatest deliberative body”:

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.

His comments came after some late-night fireworks between Rep. Jerry Nadler (D-N.Y.), who is one of the House impeachment managers, and Trump attorney Pat Cipollone.

Nadler called Trump’s legal strategy “embarrassing” and took the Senate to task after a series of party-line votes that will not allow for witnesses or new evidence:

The president is on trial in the Senate, but the Senate is on trial in the eyes of the American people. Will you vote to allow all the relevant evidence to be presented here? Or will you betray your pledge to be an impartial juror?

“So far, I’m sad to say I see a lot of senators voting for a cover-up, voting to deny witnesses, an absolutely indefensible vote, obviously a treacherous vote,” Nadler said. He also called it a “vote against the United States.”

Cipollone fired back: “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 told both of them to back off and warned others to do the same. He noted that during the 1905 impeachment trial of federal judge Charles Swayne, a senator objected to the use of the word “pettifogging” (which means “worrying too much about details that are minor or not important,” per Merriam-Webster).

“I don’t think we need to aspire to that high a standard,” Roberts said. “But I do think those addressing the Senate should remember where they are.”