Impeachment trial: Why did Pelosi use so many pens? (commentary by Richard Arenberg)
Richard Arenberg in BBC News, "This is an additional oath above their oath of office - it's to underline that this is different from the partisan and legislative procedures they normally go through. Even beyond the oath to the Constitution when they take office, they need to additionally swear to offer impartial justice in this trial."
January 16, 2020 BBC News