In a normal trial the judge presides over jury selection during the voir dire process. Jurors are excused for causes such as lack of impartiality. Does the Chief Justice of the US Supreme Court have the authority to excuse senators from a presidential impeachment if the Chief Justice determines them to be partial to one side or the other?
Can The Chief Justice Excuse Senators From The Jury In A Presidential Impeachment?
No, the jury (such as it may be) is fixed by the Constitution. Article I, Section 3, "The Senate shall have the sole Power to try all Impeachments." Trials of impeachment may include judges and other civil officers, Article 2, Section 4, where the chief justice would not be the presiding officer.
There is nothing in the Senate rules permitting the presiding officer to excuse any Senator. However, a Senator may be excused, by stating a reason, and by vote of a majority of Senators present.1
There are numerous examples in the Procedure and Guidelines for Impeachment Trials ..., including,
In the trial of Judge Charles Swayne in 1905, just before the vote was to be taken on the first article of impeachment, Senator P. C. Knox of Pennsylvania asked to be excused from voting as a result of his absence on account of illness. The Presiding Officer put the question and the Senator was excused.
A total of twenty-one requests by Senators to be excused from voting were granted during votes on the articles involving Judge Louderback.
1 PROCEDURE AND GUIDELINES FOR IMPEACHMENT TRIALS IN THE UNITED STATES SENATE, Excused from Participation in Trial or from Voting, pp. 77-78.