Pakistan, Oct. 8 -- The United States is a wonderful country with enduring traditions, powerful institutions and a strong practical constitution. Yet that system contains a dangerous contradiction. It gives one individual command of the world's most powerful military and sole authority to authorize nuclear force, but demands almost nothing about physical, mental or moral fitness beyond age, citizenship and residency.

The president is the face of the nation and an example whom millions admire, imitate and defend. Conduct affecting only a few people when committed by an ordinary citizen can reshape national standards when excused in the White House. If dishonesty, sexual misconduct or contempt for law is tolerated in the president, followe...