Conducting the trial of the president mostly as if it were a legal proceeding raised other questions, having less to do with procedure or even the chief justice’s presidential aspirations than with how the president’s guilt might be adjudicated. That is, conducting the trial as if it were a legal proceeding slanted the definition of impeachable offense toward a criminal breach of the law and away from questions of fitness, folly, or abuse of power. The House members prosecuting the president argued that because an impeachment trial takes place in the Senate, not in a judicial court, the trial wasn’t subject to a judicial court’s restrictions, say, regarding conviction—namely, certainty of guilt beyond a reasonable doubt. And, they said, the president need not have violated a specific law to be found guilty of malfeasance. Such is the broad interpretation of an impeachable offense, as Alexander Hamilton defined it in The Federalist Papers: Impeachment should “proceed from the misconduct of public men, or, in other words, from the abuse or violation of some public trust.”
The Senate thus faced tricky problems, and because there was no blueprint for the trial of a sitting president, there was something improvised about its solutions. After long debate, the Senate did concede a great deal of its authority, concluding that the chief justice could decide on the admissibility of evidence; however, it also stipulated that an individual senator could call for a vote on any of his rulings. And the chief justice was in fact allowed to cast a tie-breaking vote on two procedural questions; a motion to prevent him from casting such a vote was defeated.
Still, there were other issues to consider: For instance, would the president be compelled to appear? Johnson was not. In fact, his lawyers made sure of that, so fearful were they of what the pugnacious, scrappy chief executive might say, because he was already known for calling his enemies traitors and in some cases suggesting they be hanged. Instead, the president’s far more dignified lawyers replied to the summons.
Read more: Lessons from Andrew Johnson’s impeachment
Consider this too: Lincoln’s assassination had put his vice president, Andrew Johnson, in the White House; the country thus had no sitting vice president. Should Johnson be convicted and removed from office, then, the president pro tempore of the Senate was next in line for the job, per the Presidential Succession Act of 1796. (Today, the Speaker of the House would be next in line—and just imagine how senators might vote if they thought Speaker Pelosi would sit in the Oval Office.) Senators wanted to know whether Senator Benjamin Wade of Ohio, the president pro tempore, should be allowed to vote for Johnson’s conviction, because Wade’s future would be directly affected. But Johnson’s son-in-law was Senator David Patterson of Tennessee; wasn’t this a conflict of interest too? Yet if the Senate during the trial was still understood to be a legislative body, not a court, then each state was certainly entitled to the vote of its two senators, which is what was eventually decided.