Article 1, Section 5, Clause 2: Rules

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.

This clause establishes that each House of Congress determines its own rules of order and can punish a member for violating its rules (or for other offenses warranting punishment). A simple majority can impose punishment short of expulsion; expulsion requires a two-thirds majority. Seventeen members of Congress were expelled in 1861-1862 for siding with the Confederacy. Only three other members of Congress have actually been expelled, though many more have been investigated, and some have resigned under threat of expulsion. Reasons for considering expulsion range from treason to being a leader in the Mormon Church, which a majority of the Senate (but not the necessary two-thirds) somehow convinced themselves was “unconstitutional.”

Because of the high threshold for expulsion, the lesser penalty of formal censure has been much more commonly applied. There have been 33 members of Congress formally censured in its history.