Under the Constitution, the impending impeachment trial of President Donald Trump must be decided by senators who are, and who have sworn to be, impartial. Because some senators, such as South Carolina Sen. Lindsey Graham, have made no secret of their refusal to be impartial, the House managers prosecuting the case against the president should move for them to be disqualified from sitting in judgment, and the chief justice, as the presiding officer, should grant that motion.

There are only three requirements in the Constitution for the conduct of impeachment trials. A two-thirds majority is needed for conviction, the chief justice of the United States presides when the president is on trial, and—most importantly—“when [the senators] are sitting for that purpose [of impeachment] they shall be on Oath or Affirmation.” The oath is, of course, the requirement that the senators swear they will be impartial judges. The oath for senators, and also for the chief justice, is set forth in the Senate rules: “I solemnly swear (or affirm, as the case may be) that in all things appertaining to the trial of the impeachment of ——— ———, now pending, I will do impartial justice according to the Constitution and laws: So help me God.”