President Barack Obama has nominated a new judge to sit on the US Supreme Court - one of nine who have tenure for life, together exercising the highest legal power in the land. The BBC's Philippa Thomas in Washington reflects on the institution and its impact.
The nine US Supreme Court justices are appointed for life
It is a choice some US presidents never have a chance to make. Now Barack Obama has his second opportunity.
Last May he named Sonia Sotomayor to serve as the first Hispanic Supreme Court justice. Now he has nominated another woman - Solicitor-General Elena Kagan - who would become only the fourth female judge in the court's 220-year history.
The US Supreme Court operates in relative quiet and privacy. Its grand marble facade might face directly on to the US Capitol but its atmosphere is a world away from the political sound and fury of Congress.
Nonetheless, it wields immense power. This is the legal body which can decide who goes to the White House - as it did in 2000, with Bush v Gore.
This is the court which can fundamentally change the rules of the game - as in this January's judgement giving corporations more freedom to fund political campaigns.
And this is the court which has, in recent decades, changed the very contours of American society. Think of Roe v Wade, legalising abortion, or Brown versus the Board of Education, effectively desegregating schools.
It is both above politics and intensely politicised. Each nomination is heavily scrutinised, each presidential "pick" facing intense and sometimes hostile scrutiny from the Senate opposition. Mr Obama's new choice may relish life on the bench - but first comes a summer in the firing line.
Supreme Court analyst Nina Totenberg on the importance of the nomination
What is at stake? The very nature of the court. In the past five years, under Chief Justice John Roberts, it has shifted to the right. On that, liberal and conservative alike can agree. Ask whether this is good for America, and the argument begins.
Asked to sum up the shift in outlook, Washington's best known court-watcher, Nina Totenberg of National Public Radio (NPR), described today's court as "quite far right in its interpretation of the constitution and the law".
"We have now by a narrow five to four majority, a dramatically more conservative court than we have seen in, I would say, more than 60 years," she said.
Take January's campaign finance decision. It clearly offended Mr Obama, to the extent that a week later, he lashed out in the most high profile of settings - his annual State of the Union speech.
Here's how he put it: "Last week the Supreme Court reversed a century of law that I believe will open the floodgates to special interests to spend without limit in our elections. I don't think American elections should be bankrolled by America's most powerful interests."
John Roberts has been chief justice for the past five years
The president's decision to go public in that way clearly offended at least one justice - the conservative Samuel Alito - who was caught on camera, while sitting in the audience, shaking his head, mouthing "that's not true".
And there are potentially more battles to come between Supreme Court and White House.
What if the judges decide to take on Mr Obama's key policy initiative? NPR's Totenberg believes they could vote to invalidate key provisions of the new health bill. That would be a battle royal fought out in the court - and the watching media.
So what's the thinking behind Mr Obama's latest nomination? He knows he cannot significantly shift the court's political outlook. He is seeking, after all, to replace a liberal, in retiring Justice John Paul Stevens.
But Mr Obama can influence the panel's judicial outlook. And that is where his opponents are gearing up for a fight, concerned at the prospect of an "activist" judge.
Asked what that means, influential Republican Senator Orrin Hatch told me he wants jurists "who respect the constitution, abide by the constitution, and do not substitute their own personal views for the constitution".
SUPREME COURT LINE-UP
Sonia Sotomayor - nominated by Barack Obama 2009
Samuel Alito - George W Bush 2006
John G Roberts (Chief Justice) - George W Bush 2005
Stephen Breyer - Bill Clinton 1994
Ruth Bader Ginsburg - Bill Clinton 1993
Clarence Thomas - George H W Bush 1991
Anthony Kennedy - Ronald Reagan 1988
Antonin Scalia - Ronald Reagan 1986
John Paul Stevens (retiring) - Gerald Ford 1975
And that is the long-running struggle that lies behind this week's headlines.
To put it rather simplistically, conservatives are satisfied that the court's recent trend to the right is essentially a rebalancing act that better reflects the outlook of the nation, after the "culture wars" of the 1960s and beyond.
Liberals believe the court should do more to reflect society's evolving views, as it has done in recent decades on race relations, sexual equality and matters of religion and state.
And on similar lines, how far do you go in arguing that the individual justices should reflect today's society?
Historically, they have been white, male and mainly Protestant - fine legal minds of course, but drawn narrowly from America's educated Eastern elite.
Today, the panel includes one African-American and one Hispanic judge. There are two women and may soon be three.
What about religion? Currently, there are six Catholics, two Jews and only one Protestant - the retiring Justice Stevens. And even geography? With only one westerner on the bench, is there enough attention paid to issues like water rights and Indian affairs that loom so large in the West?
I think that since the country owns the Supreme Court, the Supreme Court ought to open itself up a little more
Tom Goldstein ScotusBlog
And as Americans consider whether the Supreme Court can fairly be said to speak for the nation, the question arises: should the voters have the chance to hear - and see - that speech for themselves?
Today, if voters want to witness the legal arguments, they have to come to Washington to queue for limited seating. In the nation which brought us Court TV, is it time to fling wide the doors of this historic institution?
Lawyer Tom Goldstein, publisher of the influential ScotusBlog, says yes.
"That's the next step, for the justices to let America see them in action. I think that since the country owns the Supreme Court, the Supreme Court ought to open itself up a little more."
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