With Friday's announcement that Associate Supreme Court Justice John Paul Stevens plans to retire at the end of this term, President Barack Obama has been handed his second opportunity within a year to shape the balance of the nation's highest court in ways that will endure long after he leaves office.

Justice Stevens is the leader of the liberal minority in a court that has become more conservative over recent decades, and Mr. Obama has already indicated that he is seeking similar qualities of mind and heart in his next appointee — what he described as "an independent mind, a record of excellence and integrity and a keen understanding of how the law affects the daily lives of ordinary people."

These were the very characteristics that led him last year to nominate Justice Sonia Sotomayor, who despite criticism from some Rebublican senators for a supposed propensity toward judicial activism, managed to win confirmation with bipartisan support on the basis of her impeccable record as an appeals court judge and unflappable demeanor during the Senate hearings. One would hope that those Republicans who ultimately supported Justice Sotomayor would apply the same standards to Mr. Obama's next nominee, but in this election year, don't count on it.

Whoever President Obama nominates to replace Justice Stevens will likely have to endure fierce attacks in the Senate, where Democrats no longer control the filibuster-proof 60-vote majority they enjoyed in 2009. Thus the stage has been set for a confirmation battle that likely will dominate the political debate in Washington for much of this summer.

In the polarized political atmosphere of Washington, getting any high court nominee confirmed will hardly be a cakewalk — the Obama administration is still awaiting confirmation for dozens of lower court judges that the Senate so far has failed to act upon. But Mr. Obama also has available a number of experienced candidates — including Solicitor General Elena Kagan and federal appeals court judges Diane Wood and Merrick Garland — whose qualifications for the job are not in doubt and who bring to the court the balance Mr. Obama is seeking to preserve. The country needs to hear the debate on maintaining that balance as much as it needs a full nine-member court operating by the beginning of next term.