William Rehnquist, the chief justice of America’s Supreme Court, has died, and President George Bush has nominated John Roberts to replace him. Since Mr Roberts had already been picked to replace another justice on the court, this means that a second high-court seat is now available. It is an opportunity conservatives have dreamed of, but it comes as Mr Bush’s political capital is at an all-time low

EVEN his ideological opponents agreed that William Rehnquist was an honest and fair-minded man who ran a tight ship as the top judge on America's Supreme Court. His death on Saturday September 3rd was, in the overused phrase, the end of an era. As chief justice for nearly 20 years, the conservative Mr Rehnquist pulled the court slowly but surely to the right, and power in America firmly away from the federal government and towards the states. How his legacy is judged is a question for future historians, but that it is significant is beyond doubt.

But even as his body lies in state in the Supreme Court building, thoughts are inevitably turning already to the future. President George Bush has nominated John Roberts to succeed Mr Rehnquist. Mr Roberts had already been nominated to an associate judgeship on the court on the retirement of Sandra Day O'Connor, a conservative who nonetheless earned a reputation as the swing voter on social matters. Mr Roberts's confirmation hearings in the Senate had been expected to begin early this week.

But that was before the latest turmoil. Not only has Hurricane Katrina shaken America (see article), causing Mr Bush to postpone, among other things, a visit by China's president. Mr Rehnquist's death means that there are now two Supreme Court vacancies, and the president's decision to nominate Mr Roberts as chief justice changes the picture further still. It was announced on Monday that his confirmation would be postponed until later this week or early next.

The chief justice has no more weight in voting than his eight colleagues. But he is the court's chief administrator, and among his more important duties is assigning opinions for his fellow justices to write. This is no small power, since the different judges have both differing politics and styles. The chief's position is important enough that Mr Rehnquist had to go through a fairly bruising confirmation hearing in 1986, even though he had already been an associate judge on the court for 15 years.

So even though Mr Roberts was widely expected to be confirmed as an associate justice, his nomination to the top spot will make activists and senators give him yet another close look. So far, they have failed to come up with anything embarrassing after combing through virtually everything he has ever written. Moreover, he is a likeable man with a formidable intellect, and is said to be more devoted to the law in the abstract than to pushing his personal conservatism.

Conservative he certainly is. He was a clerk to Mr Rehnquist in the early 1980s, and shows it. The two men shared a fondness for the tenth amendment to the constitution, and a corresponding wariness of the “commerce clause”. The tenth amendment says that all powers not explicitly given to the federal government in the constitution are reserved for the states or “the people”. Conservatives consider it the most widely, and sadly, ignored part of the entire document. In particular, those who would arrogate powers to Washington have taken advantage of the clause that allows Congress to regulate “interstate commerce”. This has been the legal basis for federal intervention in all kinds of matters not obviously related to commerce.

The Rehnquist court has fought back. Mr Rehnquist opposed a federal law banning guns from a certain radius around public schools, on the ground that Congress had no constitutional power to do this (guns and schools having no obvious connection to interstate commerce). Mr Roberts used the same reasoning to oppose a law protecting a species of toad native to California.

Liberals worry that turning the tide against the federal government will weaken its ability to protect the environment, civil rights, abortion rights and a host of other causes dear to them. In particular, they worry about Mr Roberts's stance on Roe v Wade, the 1973 decision that found a right to “privacy” in the constitution and thereby guaranteed legal abortion across the country. Mr Roberts has not said directly whether he would vote to overturn Roe, and probably won't in his confirmation hearings. But Mr Rehnquist was against Roe already. Barring surprises, Mr Roberts will take the same stance as his former boss on this and a host of other issues. The succession is thus unlikely to change the court much in the short term. And since Mr Roberts is only 50 years old, it is likely to ensure a powerful seat for many of Mr Rehnquist's ideas for decades to come.

Caught between falling approval ratings and a conservative base threatening to revolt, the president is likely to find nominating a replacement for Ms O'Connor a difficult test of his political touch

Hence all the attention turning to the question of who will replace Ms O'Connor, the swing vote. She was known for her pragmatic approach to cases, supporting some forms of affirmative action but not others, and some shows of public religion but not others. Though conservative, she was nothing like her colleagues Antonin Scalia and Clarence Thomas, who bring dogmatic, even radical, conservative arguments to bear on cases.

Whom will Mr Bush pick? Having just selected Mr Roberts in July, his shortlist is still close at hand. There is pressure on him to nominate someone who is not both white and male—especially in light of the racial divisions exposed by Hurricane Katrina (most of those too poor to leave New Orleans were black). Having rejected a “women-only” seat by replacing Ms O'Connor with Mr Roberts, to conservatives' delight, Mr Bush might now win points on the other side by choosing either a woman or a non-white this time.

There are several possibilities. Edith Clement, who seems to be rather moderate, was rumoured to be in the running for the nomination Mr Roberts eventually got. Mr Bush might appoint his close friend, the attorney-general Alberto Gonzales—but religious conservatives consider him flaky, particularly on abortion, and would cry foul. Emilio Garza, currently a federal appeals-court judge, would be a more reliably conservative Latino. Or Mr Bush could drop a bomb by nominating Janice Rogers Brown, a black woman, but also one of the most controversial conservatives on the bench. Opponents see her as an extremist ready to overturn long-established social-protection legislation—she has written that Franklin Roosevelt's New Deal “marks the triumph of our own socialist revolution”.

Anyone perceived as an extremist would face the threat of a filibuster—as few as 40 of the 100 Senate members can prevent a vote by debating endlessly. The Republicans are five seats short of the 60 needed to overturn such a ruse. In May, the two sides made a deal over a batch of Mr Bush's lower-court nominees (including Ms Rogers Brown), saying that the filibuster against judicial nominees could be preserved in the Senate rules if the minority agreed to use it only under “extreme” circumstances. But the agreement is fragile and could easily unravel from either side.

That said, the president's political capital is at an all-time low—thanks to violence in Iraq, spiralling petrol prices and the botched response to Katrina—and he may feel this is no time for a big fight. Caught between falling approval ratings and a conservative base threatening to revolt, he is likely to find nominating a replacement for Ms O'Connor a difficult test of his political touch. How he handles it could set the tone for much of his second term.