Robert L. Walker, an attorney with the D.C. firm Wiley Rein, is a former chief counsel and staff director of the Senate and House ethics committees.

If Roy Moore wins Tuesday's special election for U.S. Senate in Alabama, after he takes the oath of office the Senate will have the authority to begin an ethics investigation into allegations that Moore engaged in nonconsensual or assaultive sexual conduct going back to the 1960s. No rule or precedent would stand in the way of the Senate investigating and adjudicating the allegations against Moore through its bipartisan Select Committee on Ethics. No rule or precedent would prevent the full Senate from imposing a sanction commensurate with any proven offense. If he is elected and seated, the Senate will have the power — if it chooses to exercise it and if the evidence established through the ethics process supports the outcome — even to expel Moore.

The Senate may not "exclude" Moore — that is, refuse to swear him in and seat him — if he is elected. The Supreme Court stated in Powell v. McCormack in 1969 that, "in judging the qualifications of its members" to be sworn and seated "Congress is limited to the standing qualifications prescribed in the Constitution."

Whether Moore would keep his seat once sworn in would be subject to the Senate's application of a much more open-ended standard of conduct. Any ethics inquiry concerning Moore would examine whether he engaged in "improper conduct which may reflect upon the Senate." This is a flexible, expansive standard applied, as the Senate Ethics Manual states, to improper conduct "so notorious or reprehensible that it could discredit the institution as a whole, not just the individual, thereby invoking the Senate's inherent and constitutional right to protect its own integrity and reputation."

But before senators reach that step, they would have to confront two fundamental questions. First, does the Senate have jurisdiction over pre-Senate conduct? Yes, it does. In the expulsion case of Sen. John Smith in 1808, Sen. John Quincy Adams described the Senate's power to expel as "discretionary" and as being "without any limitation other than that which requires a concurrence of two-thirds of the votes to give it effect." More recently, in 2008, the Senate Ethics Committee addressed a complaint alleging misconduct by Sen. David Vitter prior to his Senate service. The timing of the alleged misconduct was one of several factors in the "totality of the specific circumstances" cited by the Ethics Committee in its public letter dismissing the complaint; but, by also explicitly reserving its right to reopen the case should new evidence arise, the committee was careful not to foreclose its jurisdiction over pre-Senate allegations.

The second, and harder, question is whether the Senate should exercise its ethics authority in a matter where the allegations were known to the voters before they cast their votes. This is where an understanding of regular order in a Senate ethics case becomes essential.

No matter how thoroughly the allegations about Moore have been reported in the media, the factual record put before the public through the press is not as extensive, reliable, credible or tested — from all sides — as the record developed by the Senate Ethics Committee in a preliminary inquiry and, possibly, in a public adjudicatory hearing would be. The Ethics Committee would subpoena all relevant witnesses and materials, and the Senate could compel compliance with these subpoenas through contempt proceedings. Witnesses before the committee — in the non-public preliminary inquiry phase and in any later, trial-like, adjudicatory phase — would be deposed or would testify under oath. Although not foolproof, the power of a potential perjury prosecution to elicit truthful, reliable and complete testimony should not be minimized. At any adjudicatory hearing, witnesses would be subject to exhaustive questioning by committee members and committee counsel; counsel for Moore would have a full opportunity to cross examine each witness.

Finally, the finders of fact in a Senate ethics inquiry — the six members of the Ethics Committee — would have the same exhaustive record before them before deciding whether to charge Moore with any violation and, if the matter gets to the adjudicatory phase, whether any charge is proven by clear and convincing evidence. Among the electorate on Tuesday, the extent and sources of knowledge about the allegations against Moore will vary widely from voter to voter.

If Moore is elected, his fellow senators will have the discretionary authority and power to commence ethics proceedings against him as soon as he takes his seat among them.