Article II, Section 4:
The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.
While the historical practices of Congress offer the best guide as to what behavior constitutes a high crime or misdemeanor, this principle does not necessarily preclude the development or expansion of impeachment's reach in the future. Indeed, as noted previously,1 the absence of impeachment proceedings directed against particular conduct in the past does not mean that such conduct would not be deemed impeachable in different circumstances.2 For example, certain conduct giving rise to impeachment might not have occurred or attracted notice at an earlier time. Understandings of impeachable behavior might also change over time to recognize impeachment as available for a wider range of behavior than has been previously recognized. One possibility, among others, is that impeachment may be seen as appropriate to punish violations of the law or the Constitution that lack an alternative remedy, such as redress in the federal courts.3 For example, impeachment has been proposed, but never applied, for alleged violations of constitutional and statutory requirements relating to the use of military force without congressional authorization.4
Likewise, future impeachments might shed light on unresolved issues pertinent to the impeachment process. For instance, the applicability of the Due Process Clause of the Fifth Amendment to federal impeachments is unclear. In a suit challenging his impeachment and removal from office, former Judge Alcee Hastings argued that he had a property interest in his seat and salary and the government could not deprive him of these without according him due process – including a full trial before the entire Senate.5 The U.S. District Court for the District of Columbia ruled that due process applied to impeachment proceedings.6 However, the U.S. Court of Appeals for the District of Columbia Circuit reversed and remanded the ruling7 because of the Supreme Court's intervening decision of Nixon v. United States.8 On remand, the district court dismissed the case as nonjusticiable without commenting on the merits of the due process claim.9 Presently, therefore, individual Senators themselves must decide whether the Due Process Clause applies to impeachment trials and what procedures such a requirement might entail. At times, this has led to inconsistent practices. For example, at the trial of Alcee Hastings, several Senators had been Members of the House in the previous session that voted for impeachment.10 All three recused themselves from trial to avoid the appearance of a conflict.11 In contrast, the same situation presented itself at the trials of Judge Pickering and President Clinton, but no Senators recused themselves in those cases.12