Rupert Cornwell: A small nudge towards breaking the conservative grip on the judiciary

The safe expectation is that she will form part of the liberal wing, while the swing vote will continue to belong to Anthony Kennedy

Foreigners sometimes find it hard to understand the fuss generated by the nomination of a new Justice for the United States Supreme Court. But there are two very good reasons for the sound and fury.

The first is the wide power accorded by the US constitution to the judicial branch of government headed by the Court, a power that has if anything grown of late as Congress has become more polarised and ineffectual. The second is that once he or she is confirmed, a Justice – unlike a President or member of Congress – to all intents and purposes has the job for life. This last consideration is especially relevant in the case of Elena Kagan.

Barring some surprise revelation, there appears little doubt that she will be confirmed by the Senate, where Democrats have a large majority, at least until November's mid-term elections. Ms Kagan is only 50. Were she to serve until the age of the outgoing John Paul Stevens, now 90, whom she would replace on the Court, she would be a justice until the middle of this century.

On paper, her appointment should not change the underlying ideological balance of the Court, despite some fears on the left that her relatively centrist views, especially on issues involving presidential power, might actually shift the Court a fraction to the right.

The safe expectation though is that she will form part of the Court's liberal wing, while the swing vote among the nine justices will continue to belong to Anthony Kennedy, who more often than not sides with four conservatives on the Court.

In his introduction yesterday, Mr Obama praised Ms Kagan's "fair-mindedness and record of consensus-building" – a hint of his hope that these skills, much in evidence during her stint as dean of Harvard Law School, might persuade Mr Kennedy to shift sides on occasion.

But all this is speculation, and Ms Kagan's confirmation hearings before the Senate Judiciary Committee this summer are unlikely to throw much light on the matter. Nominees usually give very little away on such occasions, and because Ms Kagan has never served as a judge, her questioners will have a very thin "paper trail" of rulings and opinions on which to go. And once installed, a justice's views can evolve in unpredictable ways. Among recent justices, Harry Blackmun, David Souter and Mr Stevens himself were all chosen by Republican presidents – but all three ended up as solid liberal votes on the Court.

If Ms Kagan is confirmed as the 112th high court justice in US history, it will be the first time that three of its members have been women. But Mr Obama will have to wait longer before he has a chance of breaking the conservative grip on the Supreme Court.

He has already made two appointments and a third vacancy may well arise before the end of his first term. But the most widely touted departure is that of another liberal, Ruth Bader Ginsburg, who is 77 and has had two bouts of cancer.