A Supreme Court with an absent and ailing chief justice is very different from a White House with an absent and ailing president. While the president embodies one entire branch of government, the chief justice merely heads another. In the two weeks that Chief Justice William H. Rehnquist, 80. has been treated for a serious form of thyroid cancer, life at the court has proceeded without a sense of crisis. The judicial function is shared by eight other people, with Justice John Paul Stevens, the senior associate justice, presiding over courtroom sessions and the justices' private conferences. The administrative tasks...