WASHINGTON – Chief Justice John Roberts admonished the House managers and the president’s counsel after a fiery back and forth during the debate over amendments to a resolution outlining the rules and format of the impeachment trial of President Donald Trump.

Roberts said he felt he had to "admonish" both sides "in equal terms 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."

Roberts reprimanded the panels amid an argument over whether former national security adviser John Bolton should be subpoenaed to testify before the Senate.

To illustrate his point about the level of civility expected in the Senate, Roberts referred to an incident from the impeachment trial of Florida District Judge Charles Swayne in 1905, when one senator took issue with a House manager using the word "pettifogging" (which is an old-fashioned term for "worrying too much about details that are minor or unimportant," according to Merriam-Webster).

"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. 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," Roberts said.

In a heated argument between Judiciary Chairman Jerry Nadler and White House counsel Pat Cipollone, Nadler said that if senators voted against calling Bolton to testify, they would be "part of the cover-up."

"Either you want the truth and you must permit the witnesses or you want a shameful cover-up. History will judge and so will the electorate," Nadler said.

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Cipollone called for Nadler to apologize to the Senate, the president and "most of all, you owe an apology to the American people."

"Mr. Nadler came up here and made false allegations against our team. He made false allegations against all of you. He accused you of a cover-up," Cipollone said. “The only one who should be embarrassed, Mr. Nadler, is you for the way you've addressed this body. This is the United States Senate. You're not in charge here."

Roberts' admonishment was his first major interjection in the trial. The chief justice strives to keep the Supreme Court above the daily political fray.

"This is his most prominent chance on the national stage to show his commitment to being a fair, neutral arbiter," said Jeffrey Rosen, president of the National Constitution Center in Philadelphia. “Chief Justice Roberts cares more than anything about the nonpartisan, institutional legitimacy of the courts."

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Contributing: Richard Wolf