Chapter 1: The Senate's Impeachment Role :
Impeachment is a very serious affair. This power of Congress is the ultimate weapon against officials of the federal government, and is a fundamental component of the constitutional system of “checks and balances.” In impeachment proceedings, the House of Representatives charges an official by approving, by majority vote, articles of impeachment. A committee of representatives, called “managers,” acts as prosecutors before the Senate. The Senate Chamber serves as the courtroom. The Senate becomes jury and judge, except in the case of presidential impeachment trials when the chief justice of the United States presides. The Constitution requires a two-thirds vote of the Senate to convict, and the penalty for an impeached official is removal from office. In some cases, disqualification from holding future offices is also imposed. There is no appeal.
[Emphasis added to highlight the roles.]
Essentially, the Chief Justice becomes a trial court judge and will do all those things a trial court judge would do and with power subject to rules of the Senate. The rules appear quite similar to a common trial and are covered, below, in the RULES OF PROCEDURE ....
The following PROCEDURE AND GUIDELINES ... refer to the Presiding Officer of the Senate. The following clarifies who that person is during the impeachment trial.
Presiding Officer of the United States Senate:
When the Senate hears an impeachment trial of the President of the United States, by the procedure established in the Constitution, the Chief Justice is designated as the presiding officer.
PROCEDURE AND GUIDELINES FOR IMPEACHMENT TRIALS IN THE UNITED STATES SENATE:
The Chief Justice as presiding officer.
IV. When the President of the United States or the Vice President of the United States, upon whom the powers and duties of the Office of President shall have devolved, shall be impeached, the Chief Justice of the United States shall preside; and in a case requiring the said Chief Justice to preside notice shall be given to him by the Presiding Officer of the Senate of the time and place fixed for the consideration of the articles of impeachment, as aforesaid, with a request to attend; and the said Chief Justice shall be administered the oath by the Presiding Officer of the Senate and shall preside over the Senate during the consideration of said articles and upon the trial of the person impeached therein.
Under some circumstances the Senate may overrule the Chief Justice.
VII. The Presiding Officer of the Senate shall direct all necessary preparations in the Senate Chamber, and the Presiding Officer on the trial shall direct all the forms of proceedings while the Senate is sitting for the purpose of trying an impeachment, and all forms during the trial not otherwise specially provided for. And the Presiding Officer on the trial may rule on all questions of evidence including, but not limited to, questions of relevancy, materiality, and redundancy of evidence and incidental questions, which ruling shall stand as the judgment of the Senate, unless some Member of the Senate shall ask that a formal vote be taken thereon, in which case it shall be submitted to the Senate for decision without debate; or he may at his option, in the first instance, submit any such question to a vote of the Members of the Senate. Upon all such questions the vote shall be taken in accordance with the Standing Rules of the Senate.
The power of the Chief Justice during impeachment trial.
XVI. All motions, objections, requests, or applications whether relating to the procedure of the Senate or relating immediately to the trial (including questions with respect to admission of evidence or other questions arising during the trial) made by the parties or their counsel shall be addressed to the Presiding Officer only, and if he, or any Senator, shall require it, they shall be committed to writing, and read at the Secretary’s table.
The right of defense to examine witnesses.
XVII. Witnesses shall be examined by one person on behalf of the party producing them, and then cross-examined by one person on the other side.
Conclusion of the trial, final vote.
XXIII. An article of impeachment shall not be divisible for the purpose of voting thereon at any time during the trial. Once voting has commenced on an article of impeachment, voting shall be continued until voting has been completed on all articles of impeachment unless the Senate adjourns for a period not to exceed one day or adjourns sine die. On the final question whether the impeachment is sustained, the yeas and nays shall be taken on each article of impeachment separately; and if the impeachment shall not, upon any of the articles presented, be sustained by the votes of two-thirds of the Members present, a judgment of acquittal shall be entered; but if the person impeached shall be convicted upon any such article by the votes of two-thirds of the Members present, the Senate shall proceed to the consideration of such other matters as may be determined to be appropriate prior to pronouncing judgment. Upon pronouncing judgement, a certified copy of such judgment shall be deposited in the office of the Secretary of State. A motion to reconsider the vote by which any article of impeachment is sustained or rejected shall not be in order
As stated above: There is no appeal. Furthermore, the Presiding Officer of the Senate (in this case, the Chief Justice) cannot overrule the vote.