Not yet a year into his first U.S. Senate term but eyeballing the Oval Office, Sen. Barack Obama in 2005 found himself with a rare opportunity: to weigh in on the nomination of a chief justice of the Supreme Court. It was a national moment, one that had occurred just 10 times since the year 1900, the most recent when Obama was only 15 years old.

It was also Obama's first chance to reveal his views on the high court's role. And, as he had with his speech at the 2004 Democratic National Convention, Obama made an audacious debut: "There is absolutely no doubt in my mind Judge [John] Roberts is qualified to sit on the highest court in the land," Obama said. "Moreover, he seems to have the comportment and the temperament that makes for a good judge. He is humble, he is personally decent, and he appears to be respectful of different points of view."

Roberts, who then sat on the D.C. Court of Appeals, had demonstrated "adherence to precedence," Obama said, "a certain modesty in reading statutes and constitutional text, a respect for procedural regularity, and an impartiality in presiding over the adversarial system."

And that was the problem.

In 95 percent of cases, Obama said, a conservative justice like Antonin Scalia and one like Ruth Bader Ginsburg, a liberal, would use "adherence to legal precedent and rules of statutory or constitutional construction" and arrive at the same verdict. In the other 5 percent, following case law and the Constitution would only get a justice so far, according to Obama.

It is no exaggeration to say that on judicial philosophy, Obama and his Republican presidential rival, John McCain, are like North and South Poles-as far apart as you can get.

McCain, a strict constitutional constructionist, believes the "role of judges is not to impose their own view as to the best policy choices for society but to faithfully and accurately determine the policy choices already made by the people and embodied in the law," his campaign website reads.

Obama believes the polar opposite. "What matters on the Supreme Court is those 5 percent of cases that are truly difficult," Obama said in his statement on the Roberts nomination. "In those cases, adherence to precedent and rules of construction and interpretation will only get you through the 25th mile of the marathon. That last mile can only be determined on the basis of one's deepest values, one's core concerns, one's broader perspectives on how the world works, and the depth and breadth of one's empathy."

The Democratic candidate's view of justice "completely displaces the dispassionate model, in which judges take an oath not to have any partiality, no matter the status of the litigant," said Wendy Long, legal counsel to the conservative Judicial Confirmation Network. "Obama is saying Lady Justice should rip off her blindfold and show 'empathy' for certain kinds of litigants before the court. That's the opposite of the American ideal of impartial justice."

Northwestern University law professor Steve Calabresi agrees: "It's a completely political vision of judging."

Also political has been Obama's record on judicial confirmation: In September 2005, he joined only 22 other senators, all Democrats, in voting against the confirmation of John Roberts. He led the charge in opposing the 5th U.S. Circuit Court of Appeals nomination of Judge Leslie Southwick, a moderate, widely praised jurist and Iraq War veteran. He opposed the nomination of Supreme Court Justice Samuel Alito, and other Bush nominees whom the American Bar Association found "well-qualified."

By contrast, McCain voted to confirm Clinton Supreme Court nominees Stephen Breyer and Ruth Bader Ginsberg. "Why?" McCain said in a May 2008 speech at Wake Forest University in North Carolina. "For the simple reason that the nominees were qualified, and it would have been petty, and partisan, and disingenuous to insist otherwise. Those nominees represented the considered judgment of the president of the United States. And under our Constitution, it is the president's call to make."

On key Supreme Court decisions, Obama and McCain have come down on opposite sides: For example, in the 2008 Boumedienne decision, the high court granted terror-war detainees held at Guantanamo Bay the right to challenge their detentions in federal court. McCain, himself a former prisoner of war, called the ruling "one of the worst decisions in the history of this country." Obama praised the decision to grant habeas corpus rights to enemy combatants.

In 2007, when the court upheld the federal partial-birth abortion ban in Gonzales v. Carhart, Obama said the ruling "signals an alarming willingness on the part of the conservative majority to disregard its prior rulings respecting a woman's medical concerns and the very personal decisions between a doctor and patient."

McCain called the decision "a victory for those who cherish the sanctity of life and integrity of the judiciary."

Like a dime balanced on its edge, the current Supreme Court could fall either way on abortion. With four conservative votes (Roberts, Scalia, Alito, and Thomas) and four reliably liberal ones (Ginsburg, Breyer, Stevens, and Souter), Justice Anthony Kennedy has often proved the swing vote. On partial-birth abortion, Roberts leaned conservative, but on the rest of the abortion issue, he is in some ways a cipher. In a first Obama term what's likely is that he would replace the two oldest members of the court-the reliably liberal John Paul Stevens, 88, and Ruth Bader Ginsberg, 75. However, a two-term Obama presidency could shift the court to the left in two ways.

First, the Illinois senator has indicated he will appoint justices in the mold of Ginsburg, who supports abortion until the last term of pregnancy. Second, Obama has pledged that his first act as president will be to sign the Freedom of Choice Act (FOCA), which would enshrine elective abortion in law and undo every state restriction of abortion. If conservatives challenge FOCA in federal court and lose, the effect would be that of an Über-Roe, brushing aside even the right of states to regulate abortion.

While Supreme Court appointments are critical in this election, some argue that more hinges on the next president's power to make lifetime appointments to the lower federal bench. On the judicial food chain just below the high court are 12 federal courts of appeal, each with jurisdiction over a specific geographical region. These are the courts of last resort for more than 99 percent of all federal cases, issuing decisions in about 50,000 cases annually, while the Supreme Court issues only about 80.

"These courts are very balanced right now," Calabresi said. "Some have a one-judge conservative majority and others a one-judge liberal majority. If Obama wins, I think it is fair to say that he could . . . flip us from having a kind of muddled, moderately-to-the-left legal system to having a decidedly left-wing legal system."

On the record

Obama

• Will appoint Supreme Court Justices in the mold of Associate Justice Ruth Bader Ginsburg

• Has said federal judges should rule with empathy toward the weak, less fortunate, or historically disenfranchised

• Has led Democratic efforts in the Senate to oppose President Bush's judicial nominees on ideological grounds, including sitting Supreme Court justices John Roberts and Samuel Alito

McCain

• Will appoint Supreme Court Justices in the mold of Chief Justice John Roberts

• Believes the role of judges is not to impose their own view as to the best policy choices for society but to apply to cases at bar the democratically determined policy choices already embodied in the law

• Voted to confirm sitting Clinton Supreme Court nominees Ruth Bader Ginsburg and Stephen Breyer