Barack Obama first explained his "empathy" test for choosing justices in voting against the nomination of John Roberts to be chief justice in 2005:

What matters on the Supreme Court is those 5 percent of cases that are truly difficult… In those 5 percent of hard cases, the constitutional text will not be directly on point. The language of the statute will not be perfectly clear. Legal process alone will not lead you to a rule of decision. In those circumstances, your decisions about whether affirmative action is an appropriate response to the history of discrimination in this country or whether a general right of privacy encompasses a more specific right of women to control their reproductive decisions or… whether a person who is disabled has the right to be accommodated so they can work alongside those who are nondisabled — in those difficult cases, the critical ingredient is supplied by what is in the judge’s heart.

Obama has repeatedly stressed the "empathy" criterion since then. Meanwhile, conservative senators and legal experts and some centrists have criticized it as a thinly veiled rationale for seeking justices who will bend the law to benefit favored classes of people. That, the critics stress, invites a cardinal violation of the judicial oath to do "equal justice to the poor and to the rich" — and to all others — not to mention the constitutional command to provide all persons "the equal protection of the laws."

Conservative Edward Whelan, head of the Ethics and Public Policy Center, recently wrote in National Review Online’s Bench Memos that "Obama’s own language shows that he is seeking judges who will favor particular classes of people" in "what he calls the ‘truly difficult’ cases but what one reasonably suspects are any cases of sufficient importance in which application of traditional legal analysis doesn’t yield the result that Obama really wants."

Ruth Marcus rejected such criticisms in her May 6 Washington Post column as an "absurd caricature" of Obama’s meaning. The president’s point, Marcus argued, is that "all judges are guided to some extent, consciously or unknowingly, by their life experience" — not that they should make legal rulings based on "the sympathy evoked by one party or the other."

Professor Orin Kerr of George Washington University Law School has posted a nuanced analysis on the Volokh Conspiracy blog that I find persuasive. "We need to recognize the important but usually overlooked differences in how different people understand the role of ambiguity in judicial decisionmaking," Kerr wrote. "Some people see legal ambiguity as a cause for careful judicial weighing; others see legal ambiguity as a trigger for judicial empowerment. I think those differences explain a lot about contemporary legal debates, including, I suspect, President Obama’s view of the Supreme Court and the role of ’empathy.’"

As Kerr details, Obama comes close to suggesting that he wants his justices to side with the "the powerless" against "the powerful" in the large number of close cases that pit individuals against big corporations, employees against employers, criminal defendants against cops, and the like.

Indeed, Obama accused then-Judge Samuel Alito of doing the converse, in voting against his Supreme Court nomination in 2006. Obama said that Alito "consistently sides on behalf of the powerful against the powerless; on behalf of a strong government or corporation against upholding Americans’ individual rights. If there is a case involving an employer and an employee and the Supreme Court has not given clear direction, he’ll rule in favor of the employer. If there’s a claim between prosecutors and defendants, if the Supreme Court has not provided a clear rule of decision, then he’ll rule in favor of the state."

In other comments, Obama has said: "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 the criteria by which I’ll be selecting my judges."

A few thoughts of my own:

First, Obama is quite right to stress that the hardest cases that reach the Supreme Court cannot be resolved by cranking the facts into a human computer who will spit out an ideologically neutral ruling. The law is often ambiguous. Very few contemporary constitutional questions are clearly answered by the original meaning of the Constitution and its amendments. And countless Supreme Court precedents — Roe v. Wade, to name just one — have departed so far from whatever the original meaning was that today’s justices must often choose between following original meaning and following precedent.

Obama is also right if he is saying that empathy for all of the people affected by a case, in the sense of coming to a sympathetic understanding of their positions, is essential to good judging.

But that’s not always what he seems to be saying. Rather than equal empathy for all, some of the Obama statements quoted above stress special empathy for "the powerless," for single mothers, for employees as against employers, for criminal defendants, and the like. How does that square with the oath to do equal justice to the poor and to the rich?

In addition, law-making is supposed to be mainly a democratic exercise driven by voters, not a judicial exercise driven by empathy for selected groups. Indeed, our laws as written already reflect the balance of interests — of empathy, if you will — that the democratic process has struck between the powerless, the powerful and other groups.

A leading example is a case often cited by Obama and other "empathy" advocates as showing that the Supreme Court’s conservatives lack empathy for the powerless. That was the 5-4 decision in 2007 against Lilly Ledbetter‘s claim that she had been a victim of pay discrimination based on sex, because she did not file her lawsuit until after the expiration of the 180-day time limit for suing that was specified in one of the two laws that she invoked, Title VII of the 1964 Civil Rights Act.

In my view, the court’s decision was probably a correct application of Title VII’s unusually short time limit. It reflected the balance that Congress had struck to encourage settlement of employment disputes by negotiation rather than litigation. The time limit was also designed to guard against employees waiting for years to bring a complaint, until after relevant evidence had been discarded and witnesses who would support the employer had died — which happens to be exactly what Ledbetter did.

All this was lost in an explosion of liberal outrage fanned by rampant distortions of the facts by the media, congressional Democrats and President Obama. They claimed, among other things, that Ledbetter had learned that she was paid less than most male colleagues long after all time limits for suing had expired, and that the evidence left no doubt that she had been a victim of gender discrimination. The first claim was flat-out false and the second was highly debatable, as I have detailed in two columns.

The near-deification of Lilly Ledbetter helped push a bill overruling the court’s decision through Congress in January. Whether the result will be to bring better justice for victims of job discrimination or to make employers more reluctant to hire women and minorities who might end up suing them remains to be seen.

Another reason to be wary of the "empathy" criterion is that decisions by justices (as well as legislators) who thought that they were helping the poor and the powerless have often had the unintended consequence of hurting a great many poor and powerless people in the long run. Examples include heavy racial affirmative action preferences for blacks and Hispanics in college admissions, judicial decisions requiring due process hearings before disruptive students can be disciplined, rent control laws, and generous welfare programs for single mothers.

To explain:

• Heavy preferences often come at the expense of better-qualified, relatively powerless whites and Asians whose family incomes are below those of the relatively affluent black and Hispanic recipients of the preferences. Such preferences have also been shown to harm many of their supposed beneficiaries, by stigmatizing the achievements of well-qualified minorities who don’t need preferences and by putting underqualified minorities at a competitive disadvantage with other students, leading to high dropout rates, extraordinarily high failure rates on bar exams, and the like.

• Judicial decisions requiring due process hearings before disruptive students can be disciplined have often had the effect of making it impossible for other students to learn. The reason is that the hearing process is so arduous that many teachers and principals see themselves as essentially powerless to get chronically disruptive students out of the classroom.

• Rent control laws, which help some lower-income tenants in the short run, hurt many more in the long run by decreasing incentives for builders and landlords to cater to the needs of low-income tenants. Such laws are also exploited by affluent people who hold on to luxury apartments for decades while paying rent far below their market value.

• And generous welfare programs for poor single parents have played a leading role in hurting the inner-city poor, by providing incentives to have children out of wedlock without working to support them. Supreme Court precedents that bar states from cutting off welfare payments without due process hearings feed the same destructive incentives.

Another problem with the "empathy" criterion is raised by Justice Ruth Bader Ginsburg‘s recent remarks in an interview with USA Today about a case in which school officials looking for pain medicine strip-searched a 13-year-old girl. Ginsburg complained that the male justices, some of whom seemed skeptical of a lawsuit seeking monetary damages from the school officials who strip-searched the girl, didn’t understand what a sensitive age that is for young females. "They have never been a 13-year-old girl," she said, in stressing the need for more female justices.

I share Justice Ginsburg’s view that Obama should add one or more women to the court. An almost-all-male court is an unfortunate symbol at a time when women are rising to parity in so many other areas of the legal world, and when many superbly qualified women are available.

But does Ginsburg’s statement, taken to its logical endpoint, suggest that female justices should tilt the law in favor of female litigants, at least some of the time?

Well, if Ginsburg’s statement means anything, it means that a strip-search might be more traumatic for a 13-year-old girl than for a 13-year-old boy. How would she know that? Unlike her colleagues, she has never been a 13-year-old boy.

There may be cases in which a female justice’s life experience might help her understand a female litigant’s problems better than male justices. But I doubt that the strip-search case was one of them. Not unless Ginsburg meant to suggest that the justices should sometimes rule in favor of strip-searched 13-year-old girls while ruling against strip-searched 13-year-old boys in otherwise identical fact patterns.

And what else could she mean?