Mr. Moore and his allies may draw some encouragement from Powell v. McCormack, a 1969 Supreme Court decision holding that the House could not refuse to seat Representative Adam Clayton Powell Jr. of New York, who had been accused of misusing House funds. The court ruled that Powell met the Constitution’s age, citizenship and residency requirements for membership in the House, and that the House could not add additional qualifications for election.

But in that same ruling, the court also said that although the House had to accept Powell, it didn’t have to keep him — it could vote to expel him. (In the end, it didn’t, though Powell lost his re-election bid in 1970.) The Senate could do the same with Mr. Moore: seat him, then immediately vote to expel him based on his lack of character and fitness to serve.

To the extent that Mr. Moore is entitled to a defense against expulsion, the Senate could initiate fitness proceedings now, before the election, to ascertain whether the accusations against him are credible; alternately, it could suspend his swearing-in until after the investigative proceedings are concluded. If Mr. Moore chose to ignore them, the Senate could simply conclude that he lacks the character and fitness to serve — as Mr. Moore, a former Alabama Supreme Court chief justice, surely knows, failing to contest an adjudicative proceeding results in a default judgment.

The Senate has precedents for this course of action. Most recently, expulsion proceedings have been contemplated against Senator Robert Menendez, Democrat of New Jersey, should he be convicted in his current corruption trial. And two former Republican senators, John Ensign of Nevada and Bob Packwood of Oregon, faced the prospect of expulsion for sexual misconduct, leading both of them to resign instead.