As Black explains, when it comes to some of the nittier procedural details, the challenge lies in determining which parts of the impeachment and trial process should be treated like their criminal law analogues, and which parts need not be. He starts with some technical examples: What should be the burden of proof, and what are the rules for the admissibility of evidence? He concludes that on both questions, logic dictates some departures from criminal law.
Take burdens of proof. In criminal cases, the jury must be convinced “beyond a reasonable doubt” on every fact required to establish guilt for the offense charged. The courts have generally declined to translate this standard into numerical terms, but that hasn’t stopped judges and scholars from attempting to quantify it: popular proposals range from an 80 percent chance of guilt to 99 percent. The point is that the standard requires a high level of certainty—in contrast with civil cases, where the verdict goes to whichever side supported by a “preponderance of the evidence”: 51 percent. Black reasons that the proper standard for finding the president guilty of an offense probably falls somewhere between the civil and criminal poles.
As for the admission of evidence, Black makes what I think amounts to a conclusive argument that the technical rules of evidence “have no place in the impeachment process.” The House and Senate should review all relevant evidence, full stop. After all, there is no way to keep “hearsay” from Congress, the way it is kept from sequestered juries. When it comes to circumstances and facts that suggest the unreliability of certain evidence, it is on the House and Senate to exercise their judgment to “appropriately discount” that evidence.
— Read on www.lawfareblog.com/impeach-president-applying-authoritative-guide-charles-black