When the president was choosing his nominee to replace Supreme Court Justice William Brennan, I hope his advisers reminded him of what happened when President Abraham Lincoln faced a similar choice. The tale is also worth the Senate's attention.

Lincoln had a Supreme Court vacancy to fill at a time when the court was about to hear the Legal Tender Cases. These cases involved the constitutionality of the Civil War statute authorizing the Treasury to issue paper money and making it "legal tender" for the payment of existing as well as future obligations. The cases were of enormous importance to the solvency of the government, and the argument was likely to turn on the vote of the new chief justice Lincoln was about to nominate.

Lincoln wrote to a friend: "We cannot ask a man what he will do, and if we should, and he should answer us, we should despise him for it. Therefore, we must take a man whose opinions are known." He then selected his secretary of the Treasury, Salmon P. Chase, who had drafted the Legal Tender bill and had urged Congress to enact it. Chase was duly confirmed, but he confounded everyone by casting the decisive vote and writing the court's opinion holding the Legal Tender Act unconstitutional.

There are two morals to the story. The first is fairly obvious. While the president and the Senate both have the duty to consider a candidate's political and legal philosophy, they press this prerogative too far, as Lincoln recognized, if they ask how he or she would decide a particular issue such as whether to overrule Roe v. Wade.

The second moral is that thanks to the "good behavior" clause of the Constitution entitling a justice once appointed to serve for life, presidents and senators who try to make certain of how a nominee will vote are often disappointed. Lincoln is not the only president who made a wrong choice. Theodore Roosevelt was openly bitter that his nominee Oliver Wendell Holmes wrote opinions restricting the sweep of Roosevelt's antitrust legislation. Dwight Eisenhower, when asked if he had made any mistakes as president, replied: "Yes, two, and they {Earl Warren and William Brennan} are both sitting on the Supreme Court." As Holmes, Warren and Brennan prove, presidents sometimes choose more wisely than they intend.

Moreover, justices usually serve more than a decade, and some, like Justices Holmes and Brennan, for more than three decades. No president or senator can predict what the important constitutional issues will be a decade or two ahead, and no nominee could reliably say now how he or she would resolve those issues. In selecting a Supreme Court justice, no president or senator with a sense of history would limit the focus to today's headline cases.

There is a further and even more important point. As Prof. Charles Black has noted, the court is the great legitimator of our government, the final arbiter of whether or not the executive and legislative branches have exceeded or abused their limited powers. To perform that vital function, the court must be, and must appear to be, as independent of the president and of Congress as humanly possible. While the president must appoint and the Senate must confirm or reject each nominee, it is vital to the integrity of the process that neither they nor the rest of us insist on knowing in advance how a new justice is going to vote in a particular case.

The key to the court's critical constitutional role lies in the mystery of its future actions. If the justices appear to have committed their votes to the president, who appoints them, or to the Senate, which confirms them, we will no longer trust them as our ultimate authority on the Constitution's meaning.

The writer, a Washington lawyer, was White House counsel to president Jimmy Carter.