Beyond what the Constitution specifies regarding impeachment trials, the Senate has established certain rules of procedure for these trials.
The Senate takes official cognizance of impeachment when formal notification by the House is delivered, though the Senate in the Johnson impeachment moved ahead with preliminary actions after the House had voted to impeach though the articles had not yet been voted.
Once the Articles of Impeachment are delivered to the Senate, according to the view that has prevailed, the Senate acts as a court, although in the impeachment of Pres. Johnson many senators and members of the House tried to avoid any idea that the Senate was acting in a judicial capacity. At this stage, the senators also agree on the basic rules by which to proceed with the impeachment.
There is no requirement that a senator be disqualified for bias or interest, although on occasion senators have voluntarily declined to vote. In the trial of Pres. Johnson, Senator Wade, the president pro tempore of the Senate, who would have succeeded to the presidency had President Johnson been convicted, was allowed to vote, and voted for conviction, while Senator Patterson of Tennessee, President Johnson's son-in-law, voted for acquittal. And Senator Sprague, who was Chief Justice Chase's son-in-law took part in the trial and voted for conviction.
The Senate has powers to carry out its constitutional authority to try impeachment including the issuance of writs, mandates, and contempt citations.
The President is not required to be present. (President Johnson did not attend but was represented by counsel.) On the other hand, the entire House of Representatives is privileged to attend and take seats in the Senate Chamber and in some cases had done so.
Oral testimony may be given before the full Senate, but the rules now provide that testimony may be taken before a committee of twelve senators.
When the trial proceeds before the full Senate, the senators act as both judge and jury. However, the Chief Justice, as presiding officer, may make initial rulings on questions of evidence subject to contrary decision by the Senate. Rule VII of the Senate Manual provides:
"And the presiding officer on the trial may rule all questions of evidence and
incidental questions, which ruling shall stand as the judgment of the Senate,
unless some members of the Senate shall ask that a formal vote be taken
thereupon, in which case, it shall be submitted to the Senate for decision, or
he may, at his option in the first instance submit any such question to a vote
of the Members of the Senate.''
As such, the senators have in effect the power to rule on objections to the admissibility of evidence.
Senators may not speak during trial. Since the Senate trying an impeachment consists, today, of up to one hundred judges, it would be too cumbersome if they were all free to question witnesses at any time. Accordingly, the rules provide that senators may put questions to a witness only in writing and through the presiding officer.
Testimony is taken in open session, but deliberations before the final votes on the Articles of Impeachment are held in closed session. The vote on the Articles is then taken in open session, with the question being put to each senator individually on each Article of Impeachment. The Presiding Office shall first state the question; thereafter each senator, as his name is called, shall rise in his place and answer guilty or not guilty.
If less than two-thirds of those present and voting (assuming the presence of a quorum) find the respondent guilty, he is acquitted of the charge and a judgment of acquittal is automatically entered. A final adjournment of the Senate as a court of impeachment without voting on an Article of Impeachment acts as an acquittal.
Conviction requires the vote of two-thirds of the members present. …