WASHINGTON (AP) -- Justice Anthony M. Kennedy, who already decides whether liberals or conservatives win the Supreme Court's most closely contested cases, is about to take on an even more influential behind-the-scenes role with the retirement of Justice John Paul Stevens.
By virtue of seniority, Justice Kennedy will inherit Justice Stevens' power to choose the author of some court opinions, an authority that historically has been used -- including in as big a case as the landmark Roe v. Wade abortion decision -- to subtly shape a ruling or preserve a tenuous majority.
The change might keep the court's most liberal justices from writing some of its biggest decisions.
An unwritten high court rule gives the senior justice in the majority, most often the chief justice, the power to assign opinions.
When the liberals win an ideologically driven case by a 5-4 vote, the court's two senior justices -- Chief Justice John G. Roberts Jr. and Justice Antonin Scalia, both conservatives -- are sure to be on the losing side. With Justice Stevens gone, Justice Kennedy now is next in line.
The overall balance of power on the court is unlikely to change, with President Obama's choice of Elena Kagan to replace the liberal-leaning Justice Stevens.
But a former Bush administration solicitor general, Paul Clement, said putting the power to assign opinions in Justice Kennedy's hands is the "single most important dynamic change" brought on by Justice Stevens' departure.
David Garrow, a Cambridge University historian who has written about the court, said the 74-year-old Justice Kennedy already writes a disproportionate share of the court's big decisions and will have even more opportunities to do so now because he can assign opinions to himself.
As if to emphasize Justice Kennedy's increasing clout, he and Justice Scalia now will sit on either side of Chief Justice Roberts when the justices take the bench for the start of their new term in October. Like most things at the court, the seating is by seniority. The justices who have been there longest sit on either side of the chief justice, who wields the gavel regardless of tenure.
Justice Scalia, on the high court since 1986, now is the longest-serving. He occasionally will get to assign an opinion, but typically not in the big cases that split the liberals and conservatives. Justice Kennedy has been on the court since 1988.
Handing an opinion to the least committed member of a narrow majority is the most obvious and important use of the assigning power, several former high court law clerks said. "You figure that justice will feel compelled to stay on board," said Michael Dorf, a former law clerk to Justice Kennedy who teaches law at Cornell University.
In an important free-speech case in 1971, the justices voted 5-4 to overturn a criminal conviction for wearing a jacket with a phrase that used a four-letter expletive to oppose the military draft. Justice William O. Douglas "immediately assigned it to John Marshall Harlan, who was clearly the weakest link," said Lucas A. "Scot" Powe Jr., a Texas law professor who was a law clerk for Douglas.
Sometimes justices have used their power in more mischievous ways.
Chief Justice Warren Burger's colleagues used to complain that he occasionally changed his vote -- after the justices declared their positions at their closed-door conferences -- just to retain the ability to assign opinions. Justice William Brennan, the court's senior member for many years, "thought Burger was manipulative in his use of the assigning power," said University of Chicago law professor Geoffrey Stone, who worked for Brennan.
When the court was deciding Roe v. Wade, several justices believed Burger was in the minority and favored upholding state restrictions on abortion, according to an account of the episode in Bob Woodward and Scott Armstrong's "The Brethren." Yet after their conference on the issue, Burger said he was assigning the opinion to Justice Harry Blackmun.
Blackmun would go on to be the court's champion of abortion rights, starting with his opinion in Roe v. Wade in 1973. But it was less clear at the time that Blackmun would so strongly endorse abortion rights, and Douglas worried about the outcome.
It's difficult to assess the effect of Justice Kennedy's new power.
His pivotal role until now -- somewhere between the more conservative and the more liberal justices -- has allowed him to dictate how far the court could go in many areas.
In 2007, for instance, Justice Kennedy was unwilling to join the four conservatives to eliminate considerations of race in voluntary efforts by public school systems to increase diversity in their classrooms.
Perhaps, Mr. Garrow said, Justice Kennedy might move away from the conservatives in close cases, knowing that disagreeing with them "would put him in the decision maker's seat."
Or, he said, Chief Justice Roberts might come to the realization that "he needs to work all the more to keep Kennedy inside the conservative tent."
Another possibility is that Justice Kennedy might keep an opinion for himself that Justice Stevens would have handed off to another liberal justice. Justice Kennedy might write the same decision more narrowly than Justices Stephen G. Breyer or Ruth Bader Ginsburg would, Mr. Dorf said.
Doug Kendall, president of the liberal-leaning interest group Constitutional Accountability Center, worries that Justice Stevens' retirement means there is "no guarantee that any of the term's biggest opinions will be written by a member of the court's left flank."
Justice Stevens, who was the senior justice beginning in 1994, was accomplished at producing 5-4 opinions that "moved the law significantly in a progressive direction," Mr. Kendall said.
With Justice Kennedy calling the shots, he said, the liberals might have to get used to smaller victories.
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