Only four senators have been convicted of crimes in the 200 plus years of the chamber's history.
Here's a handy backgrounder from the Senate Web site:
"Article I, Section 5, of the United States Constitution provides that "Each House [of Congress] may determine the Rules of its proceedings, punish its members for disorderly behavior, and, with the concurrence of two-thirds, expel a member."
Since 1789, the Senate has expelled only 15 of its entire membership. Of that number, fourteen were charged with support of the Confederacy during the Civil War. In several other cases, the Senate considered expulsion proceedings but either found the member not guilty or failed to act before the member left office. In those cases, corruption was the primary cause of complaint."
In the entire course of the Senate's history, only four members have been convicted of crimes. They were: Joseph R. Burton (1905), John Hipple Mitchell (1905), Truman H. Newberry (1920), and Harrison Williams (1981). Newberry's conviction was later overturned. Mitchell died. Burton, Newberry, and Williams resigned before the Senate could act on their expulsion."