There’s more at stake for U.S. voters in November than choosing a new leader. Looming retirements from the country’s highest court – which could break the fragile conservative hold on the bench – could give the next president the opportunity to recast the tenor of the Supreme Court for years to come.

‘The president can reach into the future in ways he can’t with other appointees,’ said Lee Epstein, a law professor with Northwestern University in Chicago.

Thomas Goldstein, a partner at Washington law firm Akin Gump, said Supreme Court appointments are a president’s most permanent influence: ‘He can appoint someone to the Supreme Court and they’ll be there for 40 years.’

And the issue hasn’t escaped voter attention. According to the Connecticut-based Quinnipiac University Polling Institute, 87 per cent of voters say the presidential power to appoint Supreme Court judges is either ‘very important’ or ‘somewhat important’ in their voting decision.

Republicans are even more concerned. A Rasmussen Reports survey in May found that 30 per cent of Republicans put judicial appointments ahead of the Iraq war, but behind the economy, as their top election concern. Only 7 per cent of Democrats felt the same way.

The current bench, a largely Republican legacy, has veered further right during the presidency of George W. Bush with the appointments of Chief Justice John Roberts and Justice Samuel Alito.

‘Conservatives have a very clear idea of the direction they want to move the Supreme Court,’ said Douglas Kendall, founder and president of the Constitutional Accountability Center, a liberal think tank. ‘The progressives, on the other hand, are mostly defending prior rulings of the court.’

The nine-member court currently has four of the most conservative judges seen since the Roosevelt years, according to a 2008 study by Richard Posner, a judge on the U.S. Court of Appeals Seventh Circuit, and William Landes, a University of Chicago law professor.

Justice Anthony Kennedy, often the swing vote in close rulings, ranks as the 10th-most conservative judge since 1937, that study found. It also discovered a cumulative effect: The more Republican appointees on the court, the more conservative each judge votes.

But it is the court’s more liberal flank that is approaching retirement. Experts estimate up to three judges could leave the court over the next few years.

Mr. Kendall said that judges John Paul Stevens, Ruth Bader Ginsburg, David Souter and Stephen Breyer are on average 15 years older than the court’s conservative bloc; Judge Stevens, for example, is 88. Mr. Kendall thinks judges Stevens and Ginsburg will retire during the next eight years and notes that Judge Souter has expressed a wish to return to his home state of New Hampshire.

It would take only one departure to shift the dynamics. ‘The court hangs in the balance of the single vote,’ said Mr. Goldstein of law firm Akin Gump.

During the 2006-07 Supreme Court session, 24 out of 68 decisions split 5-4, with Judge Kennedy casting the deciding vote each time. And while the 2007-08 session saw fewer such cases (only 11 cases split 5-4, out of 67), the decisions involved were significant. One gave Guantanamo Bay terrorism suspects access to U.S. federal courts to contest their detentions. Another overturned the District of Columbia’s ban on handguns.

Mr. Goldstein thinks that if Democrat Barack Obama were to become president, the court would likely maintain its current balance when new members are appointed. With Republican John McCain making the appointments, the court’s conservative slant would be strengthened further.

‘I will look for people in the cast of John Roberts, Samuel Alito, and my friend the late William Rehnquist – jurists of the highest calibre who know their own minds, and know the law, and know the difference,’ Mr. McCain told a crowd at North Carolina’s Wake Forest University in May.

The judges cited by the Arizona senator are among the most conservative judges in decades.

Mr. Obama, in contrast, favours those in the liberal mould of judges Ginsburg, Breyer and Souter.

‘We need somebody who’s got the heart, the empathy, to recognize what it’s like to be a young teenage mom, the empathy to understand what it’s like to be poor or African-American or gay or disabled or old – and that’s the criterion by which I’ll be selecting my judges,’ Mr. Obama said in a 2007 speech to a Planned Parenthood audience.

Experts believe a more conservative court would be more business friendly, erode abortion rights and expand the use of the death penalty.

But any presidential nominee would have to pass muster with the Senate, and many expect the chamber to be firmly in Democratic hands next year.