The authority of the United States Senate (as well as of the House) to establish the rules for its own proceedings, to 'punish' its Members for misconduct, and to expel a Member by a vote of two-thirds of Members present and voting, is provided in the Constitution at Article I, Section 5, clause 2.
The authority of the United States Senate (as well as of the House) to establish the rules for its own proceedings, to 'punish' its Members for miscon...