By Matthew Davis
BBC News, Washington
The retirement of Justice Sandra Day O'Connor from the United States Supreme Court opens a battle for the legal soul of the nation.
Justice O'Connor was the first woman to hold a seat on the Supreme Court
Originally a conservative, the 75-year-old is now seen as an open minded centrist who has voted both with the left and right leaning members of the court.
But many assume that President George W Bush will want to replace her with a conservative justice.
If such a person is approved by Congress it could swing the balance of power in the court away from the middle to the right.
This could have massive political implications for divisive issues like abortion, gay rights and medical research.
Her departure comes at a time of enormous polarisation between Democrats and Republicans, and particularly between conservative and liberal America.
President Bush faces one of the biggest decisions of his presidency to date in making the first new appointment to the court for more than a decade.
Its tight decisions on public displays of the Ten Commandments illustrated just how finely balanced the Supreme Court is at the moment.
And they also pointed to the huge changes that could be wrought by just one or two justices.
Already, forces from all parts of the political spectrum are mobilising for a fight that - while it lasts - will dominate US politics.
Pressure groups are expected to spend some $40m on vociferous campaigns, engaging millions of Americans in debate via cable television, the internet and radio.
Fight for dominance
Jay Sekulow, chief counsel for the conservative American Center for Law and Justice, is confident that Mr Bush would nominate someone who shares the president's conservative judicial philosophy to replace Justice O'Connor.
He says there has never been more of an organised lobbying effort "on our side - ever".
Ralph G Neas, president of the left-leaning People For the American Way Foundation, says the top priority of the "radical right" is gaining dominance in the Supreme Court.
That goal is more within reach than at any point in the past two decades, he believes.
"A court with more justices who share the radical legal philosophy of the far right's favorites... would reverse decades of legal and social justice accomplishments," says Mr Neas.