Article I, Section 3, Clause 6:
The Senate shall have the sole Power to try all Impeachments. When sitting for that Purpose, they shall be on Oath or Affirmation. When the President of the United States is tried, the Chief Justice shall preside: And no Person shall be convicted without the Concurrence of two thirds of the Members present.
The Senate has conducted two impeachment trials of Presidents. The first was the trial of President Andrew Johnson,1 who was impeached in the shadow of the Civil War and significant disputes with Congress over the policy of Reconstruction.2 In the first major impeachment trial of a President, the Senate formed a committee to adopt procedures for use at trial. The procedures adopted during the Johnson impeachment are largely unchanged today.3 Chief Justice Salmon Chase administered the oath to the Senate sitting as an impeachment trial and presided over the proceedings.
The primary issue at the trial was whether President Johnson's violation of the Tenure of Office Act was an impeachable offense. The statute barred the removal of federal officeholders absent Senate approval; Johnson violated it by removing Secretary of War Edwin Stanton without the Senate's consent.4 The Johnson Administration thought the law unconstitutional,5 and there was disagreement about the applicability of the Act to Stanton because he had been appointed by President Lincoln, rather than Johnson.6 Counsel for Johnson at the Senate trial argued that impeachment was inappropriate for violating a statute whose meaning was unclear and that the law itself was unconstitutional.7 The Senate voted to acquit President Johnson by one vote.8 The failure to convict Johnson seems to have established a precedent that impeachment is not appropriate for political or policy disagreements with the President; instead, impeachment is reserved for serious abuses of the office.9
The impeachment trial of President Bill Clinton was the second Senate trial of a president.10 The impeachment of President Clinton stemmed from the investigation by an independent counsel into a wide range of alleged scandals in the Clinton Administration. Independent Counsel Starr's investigation eventually expanded into whether President Clinton committed perjury regarding the existence of a sexual relationship he had with a White House staffer in his response to a civil suit and obstructed justice by encouraging others to lie about his relationship with the staffer.11
Starr referred a report to the House of Representatives on September 9, 1998, noting that under the Independent Counsel Act in effect at the time, his office was required to notify Congress about potentially impeachable behavior discovered during the course of the independent counsel investigation.12 The House eventually impeached President Clinton for perjury to a grand jury and obstruction of justice.13 In a departure from past impeachment trials of judges and executive branch officials, the Senate voted to require separate votes to approve each individual witness offered by the House managers.14 Due to the infrequency of presidential impeachments, the relevance of the Senate's decisions concerning the procedures employed in the Clinton trial for future impeachments is uncertain.
The constitutional significance of the Clinton impeachment experience is still a matter of dispute. To the extent the impeachment of President Clinton stemmed from behavior arguably unconnected to the office, some might view the ultimate acquittal of President Clinton by the Senate as evidence that impeachment only applies to behavior distinctly public in nature.15 However, the majority report of the House Judiciary Committee argued that just as perjury, for example, was an impeachable offense for a federal judge, so too was it an impeachable offense for a President because it was
just as devastating to our system of government.16 In addition, the charge of obstruction of justice brought by the House alleged that President Clinton used the powers of his office to impede and conceal the existence of evidence in both a civil lawsuit brought against him and during the investigation of the independent counsel.17 Complicating matters further, the acquittal might not represent any particular view of the standards for impeachable behavior, but simply either that the House managers did not prove their case, or that other considerations drove the votes of certain Senators.18