This ultimately redounded to Justice Thomas’s benefit. Now, whenever Ms. Hill’s sexual harassment allegations are raised, he or his defenders can at least say they were explored by the senators and ultimately found insufficient to deny Mr. Thomas a seat on the Supreme Court.

If Mr. Kavanaugh is confirmed without further investigation of Ms. Ford’s charges, he and his defenders will not even be able to claim what Mr. Thomas’s defenders can. Judge Kavanaugh will be dogged by these accusations throughout his entire, likely decades-long service on the court. And that will lead some to question the legitimacy not just of his appointment but of the court as an institution — especially when it decides knotty social and political issues by a 5-4 vote.

Considering the small number of witnesses involved — perhaps Ms. Ford, Mr. Kavanaugh, Mr. Judge, Ms. Ford’s husband and her therapist — an F.B.I. investigation followed by hearings wouldn’t take very long. The process might not be complete before the start of the Supreme Court’s new term on Oct. 1, but it should easily be able to be done before the midterm elections, if that’s the concern of Senate Republicans.