Sen. Mike Lee, R-Utah, maintains that senators are "absolutely not jurors" during an impeachment trial.
Lee made his comments on Tuesday in a column posted by Fox News.
He said the Constitution "sets impeachment apart from jury trials" by noting that "'the trial of all crimes, except in cases of impeachment, shall be by jury.'"
"The authors of the Constitution knew impeachment — for good or ill — was an inherently political act," he said. "James Wilson, one of the nation's first Supreme Court justices and one of the principal architects of the Constitution, described impeachment as 'confined to political characters, to political crimes and misdemeanors, and to political punishments.'
"By its very nature, the Senate's role in the impeachment process clearly indicates that senators are not passive observers of the trial. The Constitution gives the Senate the sole power to set its own rules.
"Under the Senate's long-established impeachment rules, senators decide what evidence should be heard, how it should be presented and what witnesses should (or should not) be called. They can even override the presiding officer, who in the case of a presidential impeachment is the chief justice."
Lee argued that "no jury can do that."
He also noted jurors in trials are generally precluded from serving if they know one another or the defendant.
"We, therefore, must not confuse the role of a jury with that of the Senate in an impeachment trial," Lee wrote.