If you ask Americans what issues matter most to them in choosing a president, the candidate's judicial philosophy is not likely to make it into the top 10. But a president's power to nominate judges is, in fact, one of his most powerful tools -- and often leaves a legacy that lasts far longer than any policy initiative.

President Dwight Eisenhower was no liberal activist, but his appointment of Earl Warren as chief justice of the U.S. Supreme Court dramatically shifted the nation leftward for decades on everything from criminal justice to separation of church and state to legislative reapportionment. Similarly, President Ronald Reagan was far more successful in reshaping the courts than in reducing the size of government. So it's important to know how each of the current candidates will go about picking judges when one of them becomes president.

Both Barack Obama and Hillary Clinton are graduates of Ivy League law schools, Harvard and Yale respectively, and Obama taught constitutional law for a decade. Both approach the Constitution as a "living document," which they believe must constantly be interpreted anew depending on changing circumstances, mores, and values. The literal meaning of the words themselves are no more important in their eyes than the judge's interpretation of what is right and just. Thus, the 14th Amendment's guarantee of equal protection under the law without regard to race or color can be interpreted to permit discrimination against whites if it benefits blacks or Hispanics because, as a group, the latter have faced discrimination in the past and remain, on average, economically disadvantaged.

Given this philosophy it's no wonder that Barack Obama set out his criteria for picking judges this way. "We need somebody who's got the heart … the empathy to recognize what it's like to be a young teenage mom, the empathy to understand what it's like to be poor or African-American or gay or disabled or old. And that's going to be the criteria by which I'm going to be selecting my judges." When Obama voted against Justice Samuel Alito's nomination to the Supreme Court, he said it was because Alito's record showed "extraordinarily consistent support for the powerful against the powerless." In other words, a judge's role should be to decide which party should prevail on the basis of some abstract notion of fairness.

Now, this might strike some people as a good thing -- though I can't for the life of me figure out why anyone should have to go to law school or have any familiarity with legal principles and precedents in order to become a judge if compassion is the chief criterion on which cases should be decided.

Hillary Clinton's list was a little more substantive than Obama's. She told attendees to a 2007 Planned Parenthood convention that she would pick judges who "understand the role of precedent," by which she meant Roe v. Wade -- though, apparently, no decision after it that rolled back an unlimited right to abortion. But she also threw in the phrase "well-qualified judges," which, at least, acknowledged that she would require something more than a kind heart in making her selections.

Ironically, the only candidate whose primary concern is the law is the one candidate who isn't a lawyer: John McCain. He says he wants "jurists of the highest caliber, who know their own minds, and know the law, and know the difference." Perhaps it takes the humility of one who hasn't gone to law school to hold the law in such high esteem. More likely, it's respect for the democratic process by which the people choose lawmakers. In McCain's view, it's the role of the Legislature -- made up of the people's elected representatives -- to write laws. If the people don't like the laws their representatives make, they can pick new legislators, but neither the people nor legislators should rely on judges to rewrite those laws for them.

It's impossible to predict a future president's judicial picks, but it's an almost certain bet that a President Obama (or Clinton) would choose judges who share their expansive view of judicial power while a President McCain would choose more humble judges who understand the limits of that power. What remains is for the voters to decide how much power they are willing to turn over to unelected men and women with lifetime tenure -- and pick their president accordingly.