For the first time in nearly 20 years, William Rehnquist is not presiding over a new session of the Supreme Court. The 80-year-old chief justice announced in late October that he is suffering from thyroid cancer. After undergoing a tracheotomy to help him breathe more easily, Mr. Rehnquist said he would not participate in a dozen pending cases, unless his colleagues are facing a 4-4 split vote. Though he plans to administer the oath of office at President Bush's second inauguration on Jan. 20, Mr. Rehnquist's longer-term plans are unknown. Without a retirement announcement, the White House has remained mum on a possible replacement, but rumors name Justice Clarence Thomas as the front-runner for the chief's stripes.