WASHINGTON -- Justice Samuel A. Alito Jr. - who was quietly sworn in yesterday as the 110th justice of the Supreme Court - will have only one vote, of course. But it could be the decisive one in several of the marquee cases that will dominate the balance of the Supreme Court's term.
By the end of the term in early summer, legal analysts said, the nation will most likely have a good sense of whether Alito will affirm or veer away from the direction set by his predecessor, Justice Sandra Day O'Connor, in cases involving the treatment of terrorism suspects and campaign finance. Alito was confirmed yesterday by a 58-42 Senate vote.
A first taste of how his legal views on abortion, a signature issue for O'Connor, might differ from hers could come before the end of the year. And other issues on which O'Connor was often the swing vote, including affirmative action and religion, are certain to reach the court in coming years.
"Justice O'Connor's seat is the tipping point on a range of hot-button issues that the Supreme Court confronts every year, including at least a half a dozen cases the Supreme Court is still to confront this term," said Thomas C. Goldstein, a Washington lawyer who often appears before the court.
In other cases, though, Alito's votes will probably have only a limited impact. He is expected to join the three justices considered conservative - Chief Justice John G. Roberts Jr. and Justices Antonin Scalia and Clarence Thomas - to form a voting bloc of four. Balancing that is a four-member liberal bloc made up of Justices John Paul Stevens, David H. Souter, Ruth Bader Ginsburg and Stephen G. Breyer.
That leaves Justice Anthony M. Kennedy as the new fulcrum.
"We changed from a court split 4-3, with two in the middle," said Richard Epstein, a law professor at the University of Chicago, referring to the dual swing votes of O'Connor and Kennedy. "Now it's 4-1-4, and now it's Kennedy."
Kennedy seems poised to be the court's crucial vote in cases involving gay rights, the government taking of private property and aspects of the death penalty.
There are, however, several important cases where Alito's replacement of O'Connor will put him in the spotlight.
The court will soon decide, for instance, whether to hear a case concerning the constitutionality of the federal Partial-Birth Abortion Act of 2003, which would outlaw an abortion procedure. The law is quite similar to a Nebraska law struck down in 2000 by a 5-4 vote in Stenberg v. Carhart, with O'Connor in the majority.
"Here, the difference between O'Connor and Alito is widely expected to be decisive," said Erwin Chemerinsky, a law professor at Duke University.
There is no case on the horizon, however, that attacks the core of Roe v. Wade, the 1973 decision that found a constitutional right to abortion. Nor does it seem that Alito would play a determinative role in such a case in any event, given what is known about the other justices' views. The court's lineup had stood at 6-3 in favor of fundamental abortion rights before the death of Chief Justice William H. Rehnquist and the retirement of O'Connor.
Since Rehnquist was in the minority, his replacement by Roberts would not alter the balance if the new chief justice opposes abortion rights. Unless someone switches sides, then, Alito could do no more than add a fourth dissenting vote.
Kennedy was in the majority in Planned Parenthood v. Casey, a 1992 decision that affirmed Roe's core, but he dissented in Stenberg, the Nebraska case.
"The question now," said Pamela S. Karlan, a law professor at Stanford, "is, what's Kennedy's position going to be?"
Alito will almost immediately begin work on two complex terrorism cases. Each revisits aspects of the trilogy of 2004 cases in which the Supreme Court, with O'Connor in the majority, refused to endorse the Bush administration's broadest claim that people detained as terrorism suspects were not entitled to challenge their detentions in the courts.
The court is scheduled to hear arguments in March in the case of Salim Ahmed Hamdan, a Yemeni detainee at Guantanamo Bay, Cuba, who has challenged the military commissions the administration has created to try terror suspects. Roberts ruled against Hamdan in July as a judge on the federal appeals court in Washington, and he will not participate in the case in the Supreme Court. That makes Alito's role that much more prominent.
"With Roberts recused," Chemerinsky of Duke University said, "you have more of the possibility that Alito will have the decisive vote." Another possibility is a 4-4 tie, which affirms the lower court's decision but does not establish a precedent.
After the Supreme Court agreed to hear the Hamdan case, President Bush signed a law that might prohibit the court from considering it. It is not clear whether the law applies retroactively and, if it does, whether it is constitutional.
The court is also considering whether to hear an appeal from Jose Padilla, a U.S. citizen suspected of planning a terrorist attack who was held by the military for almost three years without charges. Not long after Padilla filed his appeal, the government transferred him from military custody to face criminal charges and urged the Supreme Court not to hear the appeal, arguing that it was moot.
In both the Hamdan and Padilla cases, said David A. Strauss, a law professor at the University of Chicago, there is reason to think that Alito will be more sympathetic to the government's arguments than O'Connor would have been.
The vote on Alito's nomination was unusually close and partisan. In the past 100 years of Supreme Court confirmations, only one vote was closer: the 52-48 decision to confirm Clarence Thomas in 1991.
In this confirmation, 54 Republicans voted for Alito, and just one, Sen. Lincoln Chafee of Rhode Island, voted against him. Only four Democrats - Sens. Ben Nelson of Nebraska, Kent Conrad of North Dakota, Tim Johnson of South Dakota and Robert C. Byrd of West Virginia - voted for confirmation. The other 40 Democrats and one independent voted against it.