By confirming each House's power to set its own procedures, the Framers strengthened the independence of each branch of Congress against the other as well as against the executive and the judiciary. Although the original proposal to give each House of Congress the power to expel lacked a supermajority requirement, James Madison, pointing out the danger that a majority faction could abuse its power by expelling Members of the minority, successfully moved to insert the two-thirds rule. Unlike the exclusion power of Article I, Section 5, Clause 1, there are no judicially enforceable constitutional standards limiting the use of the expulsion power other than the supermajority requirement. In re Chapman (1897). Moreover, the courts generally regard disputes arising from the procedural rules of Congress as nonjusticiable, unless Congress "ignores constitutional restraints or violates fundamental rights." United States v. Ballin (1892). Powell v. McCormack (1969), for example, assumed that the case would be nonjusticiable if two-thirds of the House had "expelled" Congressman Adam Clayton Powell instead of "excluding" him.
The Rules and Expulsion Clause stands as the analog to the impeachment clauses. It is the only constitutional mechanism by which a sitting Member of Congress can be removed from office. Alexander Hamilton assumed that Members of the legislature could be impeached, and some comments in the ratifying conventions presumed the same, but historical practice has been to the contrary. In 1797, the Senate expelled William Blount, but it later refused to convict him on a bill of impeachment because it concluded that there was a lack of jurisdiction. Subsequent interpretation of the Senate's action, supported in particular by Justice Joseph Story, has found the Senate's action dispositive: Members of each branch of Congress may be expelled by their own respective body, but they cannot be impeached. Story's position is supported at least in part by the text of the Constitution. The existence of the specific removal provisions for Members of Congress negates any inference that impeachment exists as an alternative removal mechanism.
Since 1789, the Senate has had nine expulsion proceedings out of which fifteen Senators were expelled, most of them early in the Civil War on grounds of supporting the rebellion. The House has also proceeded against twenty-nine of its Members but has expelled only five, two for corruption and three for supporting the rebellion.
More frequent have been instances when each House has punished its respective Members by a simple majority. Punishments have included censure (or the somewhat lesser "denouncement"), reprimand, loss of seniority, removal from committee or subcommittee chairmanship, and fine. In addition, when a Member of Congress is convicted of a crime, he is expected to refrain from voting unless and until his conviction is overturned or he is re-elected.
https://www.heritage.org/constitution/#!/articles/1/essays/22/rules-and-expulsion-clause