The historic vote in the House of Representatives on the two articles of impeachment featured a lot of disagreement about what rises to the level of an impeachable offense. But it's arguably an academic issue. Impeachment by the full Democrat-controlled House doesn't change the near certainty of acquittal at trial in the Republican-controlled Senate.
Does should that eventual outcome change the decision-making process of members of the House? Put another way, should the likely "not guilty" verdict in the Senate have influenced House Democrats' choice to vote "yay" or "nay"?
The concept of a burden of proof is embodied in the due process clause, and its function is instructing a court or jury about the degree of confidence we should have about factual conclusions. Unlike the criminal and civil judicial system, there is no explicit "burden of proof" for impeachment by the House or conviction by the Senate.
There is only the requirement of a simple majority in the House and two-thirds majority in the Senate for conviction and removal of the president.
Those headcount requirements are fundamentally different from the concept of the burden of proof, however.
In the criminal context, an indictment — an accusation — is a finding of "probable cause that a crime has been committed, and that the accused is reasonably believed to have committed it." The burden to accuse is lower than the burden to convict, which increases considerably at trial.
At trial, the prosecution must prove guilt "beyond a reasonable doubt." This is not proof beyond all possible doubt or to a mathematical certainty. Rather, reasonable doubt is a fair doubt based on reason, logic, common sense, or experience.
The Constitution give no such explicit guidance for impeachment proceedings.
Should members of the House simply have adopted the "probable cause" standard? Or is "any evidence" of an impeachable offense? Or is impeachment so weighty that the "beyond a reasonable doubt" standard should be applied in the House, just to vote "yay" on the accusation?
It seems to be totally up to individual members. Even if an individual member of the House decides on a burden that will guide her or him, how should that member have factored in the likelihood that the president will be acquitted in the Senate?
An interesting analogy exists in the Justice Manual, the Department of Justice's procedures for prosecution. These internal policies suggest that, at least in some situations, the prosecutor must believe the defendant's conduct constitutes a federal offense, and that the admissible evidence probably will be sufficient to obtain and sustain a conviction by an unbiased trier of fact.
The Manual does not have the force of law, and it is not binding on United States attorneys. It is designed to serve as little more than a guide to their conduct. Still, it suggests that federal prosecutors should have more faith in their case than just whatever is needed to get a grand jury to indict.
For members of the House, as long as they satisfy whatever burden they apply to impeach — the loose equivalent of an indictment — should it also have mattered that they don't believe there will be a conviction? Government prosecutors will say that they won't indict unless they believe they can convict. Should members of the House have employed a different standard?
The House members' duties ended upon impeachment (unless they are among the House managers taking part in the Senate trial). If their duty doesn't extend to the Senate process, there's an argument that they should not even consider what would happen there. The practical reality is that each member of the House just applies their own personal burden of proof and weighs the probable Senate outcome as they see fit.
It's a constitutionally acceptable standard. It's also a standard that would never survive in the criminal justice system, over in the judicial branch.