WASHINGTON (Reuters) - The next U.S. president could reshape the Supreme Court, where the two oldest members are liberals and volatile decisions like abortion now hinge on a single swing vote.
The possible sea change has already surfaced 18 months before the November 2008 election and could develop into a major campaign issue for Democrats who want to move the court to the left and Republicans who hope to plant it firmly in the conservative camp.
The U.S. high court is now evenly split between conservative and liberal justices, who have been divided by 5-4 votes on abortion rights, the death penalty and the environment.
Duke University law professor Erwin Chemerinsky predicts the next president probably will get two or three Supreme Court appointments. "They will determine the results in countless issues, like abortion rights," he said.
Supreme Court justices have lifetime tenure, and no one knows when the next vacancy will occur.
But the court's oldest members are liberal Justices John Paul Stevens, 87, and Ruth Bader Ginsburg, 74. The court's other two liberals are Justices David Souter and Stephen Breyer.
The swing vote belongs to Justice Anthony Kennedy, a moderate conservative. He has cast the decisive vote for abortion restrictions and for the death penalty, but against the Bush administration on global warming and on military tribunals for Guantanamo prisoners.
The shift in the court, so influential in arbitrating U.S. social and other policies, occurred after President George W. Bush's appointment of conservative Justice Samuel Alito. He replaced the more moderate Justice Sandra Day O'Connor, who resigned.
Bush also named Chief Justice John Roberts, who replaced another conservative, the late Chief Justice William Rehnquist. Conservatives hope Roberts will lead the court to the right over the long term.
A Washington lawyer who closely tracks the high court says the decisions on major social issues like abortion, affirmative action, gay rights and the death penalty will likely motivate voters more in this upcoming election than in the past.
"Interest in the court will be even higher given its recent turn further to the right," said attorney Tom Goldstein.
Abortion is already a campaign issue, with the top Republican presidential contenders supporting last month's Supreme Court ruling that banned certain kinds of abortions while leading Democratic candidates denounced it.
"This decision by the Supreme Court is actually a perfect example of what will be at stake in this election," former Sen. John Edwards said at the first Democratic debate.
Democratic Sen. Hillary Rodham Clinton of New York sent an e-mail to supporters saying the ruling "raised the stakes even higher" in terms of the importance of the election.
For Republicans, former New York Mayor Rudolph Giuliani has struggled in the past few weeks to explain his position on abortion and the Supreme Court's landmark Roe v. Wade decision in 1973 that women have a constitutional right to an abortion.
"I ultimately do believe in a woman's right of choice, but I think that there are ways in which we can reduce abortions," Giuliani said at the second Republican debate.
His support for abortion rights contrasts with his main rivals, Sen. John McCain of Arizona and Massachusetts Gov. Mitt Romney. Conservatives view overturning the abortion ruling and judicial appointments as key election issues.
Theodore Olson, formerly the Bush administration's chief advocate before the Supreme Court and a colleague of Giuliani's in the Reagan administration Justice Department, sought to reassure conservatives about the former U.S. attorney.
Olson wrote in a recent article in the National Review that Giuliani would appoint jurists in the mold of the Supreme Court's four conservatives -- Roberts and Alito and Justices Antonin Scalia and Clarence Thomas.