In the predawn hours Wednesday, Chief Justice John Roberts, the presiding officer at the impeachment trial of President Donald Trump, asserted his voice forcefully for the first time during the Senate proceedings to warn the lawyers for both sides to watch their language.

The chief justice’s remarks came after a terse exchange between Rep. Jerry Nadler, D-New York, one of the House managers, and Pat Cipollone, the White House counsel who is leading the Trump defense team.