The evidentiary standard used in congressional expulsion hearings is lower than the standard used in criminal court cases. “In the disciplinary process generally, not just at an expulsion hearing, to find that there has been a violation of Senate ethics rules, the evidence has to reach the level of clear and convincing evidence,” says Walker.

What’s the definition of “clear and convincing” evidence? “All I can tell you is that ‘clear and convincing’ evidence is a standard somewhere between ‘probable cause’ and ‘proof beyond a reasonable doubt,'” says Walker. “It’s an evaluation that’s up to the finders of fact in any given matter, and in an ethics matter, that would be the members of the Senate Ethics Committee.” The standard of “clear and convincing” evidence is also a higher standard than “preponderance of evidence.”