Each House may determine the Rules of its Proceedings, punish its Members for disorderly Behaviour, and, with the Concurrence of two thirds, expel a Member.
Expulsion cases have been rare. As of 2017, a total twenty Members of Congress have been expelled from their respective bodies—five in the House and fifteen in the Senate. While the grounds for expulsions may illustrate potential bases upon which the House or Senate may decide to expel a Member, they are not necessarily the exclusive grounds for expulsion as this is left to the discretion of the respective bodies of Congress. Accordingly, expulsion is "'in its very nature discretionary, that is, it is impossible to specify beforehand all the causes for which a member ought to be expelled; and, therefore, in the exercise of this power, in each particular case, a legislative body should be governed by the strictest justice.’" Expulsion does not appear to apply automatically to any particular conduct.
Disloyalty to the United States appears to be the predominant basis upon which both the House and Senate have exercised their power to expel Members. Eighteen of the twenty expulsions in congressional history were based on the Members’ disloyalty to the United States. The earliest expulsion case in 1797 involved a Senator who "concocted a scheme for Indians and frontiersmen to attack Spanish Florida and Louisiana, in order to transfer those territories to Great Britain" for his own financial gain. The Senate special committee that was appointed to investigate the matter recommended expulsion, describing the Senator’s conduct as "entirely inconsistent with his public trust," and the full Senate subsequently voted to expel the Member by a vote of 25-1.
The majority of expulsion cases based on disloyalty to the United States—seventeen of the eighteen—arose in the context of the secession of the Confederate states at the beginning of the Civil War. In early 1861, the Senate considered the status of Members representing states that were contemplating secession, ultimately expelling ten Members in a single vote after the war had begun. In those cases, the Members represented Southern states that had seceded from the Union, and the Members had not formally resigned from the Senate. The expulsion resolution cited the Members’ failure to appear in the Senate and alleged that the Members "are engaged in said conspiracy for the destruction of the Union and Government, or, with full knowledge of such conspiracy, have failed to advise the Government of its progress or aid in its suppression." Other examples of Civil War expulsions involved Members who had supported secessionists despite representing states that had not seceded.
After the Civil War expulsions, neither the House nor Senate expelled a Member for more than a century. In 1980, a Member was expelled following a criminal conviction on charges relating to receiving a payment in return for promising to use official influence on legislation in the so-called ABSCAM investigation. In 2002, the House expelled a Member who had been convicted of various criminal charges relating to his official actions in Congress, including bribery, illegal gratuities, obstruction of justice, defrauding the government, filing false tax returns, and racketeering.
In some cases, Members’ behavior has drawn public calls for expulsion or preliminary proceedings by the respective house toward potential expulsion, but the Member ultimately resigned prior to a formal decision to expel. Members have resigned facing formal expulsion inquiries or even recommendations for expulsion for conduct during their time in office. In the Senate, one such example occurred in 1995 when the Select Committee on Ethics recommended expelling a Member following its investigation of allegations of sexual misconduct, misuse of official staff, and attempts to interfere with the Committee’s inquiry. In the House, for example, the Committee on Standards of Official Conduct recommended expelling a Member for conduct violations related to activities that also resulted in the Member’s criminal conviction for accepting illegal gratuities, illegal trafficking, and obstruction of justice.
Abscam’s focus shifted to political corruption, and over the next year the FBI videotaped a series of meetings with politicians, predominantly Democrats from the northeast. Officials such as U.S. Representatives Raymond Lederer and Michael Myers of Pennsylvania promised to ease the sheikh’s immigration troubles in exchange for cash.
Sen. Harrison Williams, Jr., of New Jersey offered to assist Abscam’s second fictional sheikh, Yassir Habib, in return for the promise of a multimillion-dollar investment in a titanium mine in which Williams held an undisclosed financial interest. In February 1980, while the investigation was still active, word of its existence was leaked to the press.