In 1952, a young Supreme Court clerk wrote a memorandum that would come to haunt him. The court was considering Brown v. Board of Education, the great school desegregation case. The question for the justices was whether to overrulePlessy v. Ferguson, the 1896 decision that said “separate but equal” facilities were constitutional.

The memo, prepared for Justice Robert H. Jackson, was written in the first person and bore the clerk’s initials — “WHR,” forWilliam H. Rehnquist. “I realize it is an unpopular and unhumanitarian position, for which I have been excoriated by ‘liberal’ colleagues,” Mr. Rehnquist wrote, “but I think Plessy v. Ferguson was right and should be reaffirmed.”

The memo was disclosed by Newsweek in 1971, on the eve of the Senate floor debate on Mr. Rehnquist’s nomination to the Supreme Court. It caused a firestorm, one that was rekindled when President Ronald Reagan nominated Justice Rehnquist to be chief justice in 1986.

Opposition to the Brown decision is a good way to doom a Supreme Court nomination. But Mr. Rehnquist had an explanation, which he sent to the Senate Judiciary Committee in a letter in 1971 and repeated under oath in 1986.

The opinions expressed in the memo, he said, were not his own. “I believe that the memorandum was prepared by me as a statement of Justice Jackson’s tentative views for his own use,” Mr. Rehnquist wrote.

Quite a bit of evidence has accumulated over the years to cast doubt on that explanation, and now there is more.