Rupert Cornwell: Supreme Court will miss its impish inquisitor-in-chief

One of the lesser known pleasures of Washington is a visit to a neo-classical, white marble building just behind the Capitol, whose façade bears the imposing words, "Equal Justice Under The Law". There, on many Mondays, Tuesdays and Wednesdays during the winter months, you may attend oral arguments before the Supreme Court of the United States. Pick your day wisely and get in the queue early, and you can hear for free the finest legal minds in the country fighting a case that may change the future of the country – as, for example, one entitled Bush v Gore, heard in December 2000.

Each of the nine justices has his or her own methods of questioning (apart, that is, from Justice Clarence Thomas who never asks a question at all). But for the past 35 years a white-haired man, with a bow tie and an impish smile to set off his plain black robe, has been a fixture on the rostrum. Usually, he waits until midway through the hour-long session before joining the fray. "May I ask you this?" he inquires of one of the advocate lawyers with deceptive casualness, before thrusting a verbal rapier into the very heart of the case.

That justice is John Paul Stevens, who was named to the court in remote 1975, when Gerald Ford was president. On Friday, however, Stevens, who turns 90 in a few days, finally announced he would be retiring. In a country where the law is king, any change of Supreme Court justice is what a Washington Post columnist yesterday described as a "blot-out-the-sun" moment. Hyperbole aside, however, the departure of Stevens at the end of the current court term will truly be the end of an era.

Depending on the exact date the court begins its summer recess, he will have been either the second or third longest serving justice in its 221-year history. Regular tennis and a healthy diet, Stevens says, are the secret of his professional longevity and his undimmed mind – as well as the fact that, by his own admission, he spends as much time as possible in Florida, doing much of his court business by fax, phone and email.

His life is an eclectic sampling of American history. Stevens was there at Wrigley Field in his native Chicago to watch Babe Ruth hit his legendary "called shot" home run in the 1932 baseball World Series. He is almost the last person active in the highest echelons of US public life to have served in the Second World War. His reputation as a corruption fighter in his days as a federal judge in corruption-ridden Chicago was a prime reason that Ford picked him for the Supreme Court, at a moment when Watergate was fresh in everybody's mind.

Above all, though, Stevens is a symbol of how far the court has shifted to the right in the past 35 years, and how the installation of one of its members has turned from a political quasi-coronation into a brutal contact sport. When he was confirmed, the Senate vote was 98-0. Now, even a relatively uncontentious candidate will automatically attract 30 or 40 nays.

When he joined he was a moderate Republican, who slotted naturally into the centre of the court. Over the years, Stevens didn't change much, but the Supreme Court did. Moderate Republicans these days are a species facing extinction. The old liberals on the court fell away, replaced by increasingly doctrinaire and aggressive conservatives. For the past 15 or so years, Stevens has been de facto leader of its four-justice liberal minority – but with a rare gift for coalition building that could often attract a crucial fifth swing vote.

That was how, for example, the majorities emerged to challenge the George W Bush administration's denial of basic legal rights to detainees at Guantanamo Bay and elsewhere. Equally often, though, Stevens was on the losing side, as when the Supreme Court cast aside any pretence of political neutrality and handed the 2000 election to Bush. The noblest (and angriest) lines in that judicial debacle came in Stevens's dissent: "Although we may never know with complete certainty the identity of the winner of this year's election, the identity of the loser is perfectly clear. It is the nation's confidence in the judge as an impartial guardian of the rule of law."

The last straw seems to have been this year's ruling opening the floodgates for corporate spending on political campaign advertising, reversing two decades of established jurisprudence – and in most people's view, simple common sense. Stevens was so appalled that he wrote a 90-page dissent which he read from the bench himself. In doing so, however, he repeatedly stumbled over words. For almost the first time, he betrayed his age. Three months later, he announced he would retire.

In the next few weeks, President Obama will pick a successor. But with important mid-term elections due in November, the fuss this time may be greater than ever. Speculation over Stevens' replacement will fill acres of newsprint and endless hours of talk on cable TV. Learned articles will be written, interest groups of every hue will mount ferocious campaigns for and against the eventual nominee. Threats and dark rumours will be floated, bitter words will be hurled on the floor of the Senate.

But at the end of the day somebody will be confirmed – and, to be honest, it doesn't greatly matter who. Stevens will be replaced by another liberal, by a 60-40 or 65-35 majority in the Senate, but the court's balance will remain tilted to the right. It may, moreover, stay that way for a while. The logical replacement for Stevens as the court's pre-eminent liberal is Ruth Bader Ginsburg. But she is 77, with her share of health problems, and has shown little special adeptness at coalition building. John Paul Stevens, in other words, will be sorely missed. But who can begrudge him the warm days in Florida? He's earned them.