Approaching the end of 34 years on the U.S. Supreme Court, Justice John Paul Stevens has become known as an influential broker of split decisions. From 2004 to 2008, for instance, he rallied majorities to reject key elements of the Bush administration’s repressive legal tactics in the war on terror.

Stevens has used salesmanship and political skills to align moderates like Justice Anthony Kennedy and former Justice Sandra Day O’Connor with the court’s liberal wing. In a profile of Stevens for the New Yorker, writer Jeffrey Toobin called him “the undisputed leader of the resistance against the conservatives on the court.”

In announcing his plan to step down at the end of the court’s current term, Stevens seems to have once again made a shrewd tactical move to preserve the court’s balance.

He has provided a good window for the administration to choose and promote a candidate for appointment to the court. Potential picks are already under wide discussion, so those who might want to drag out the process will have a hard time claiming that consideration has been rushed.

Good timing is important, given the clear possibility that Democrats may lose seats in the Senate this fall. Today’s substantial Democratic majority in the Senate gives President Obama a reasonable chance to appoint a liberal justice and defeat any effort by opponents to filibuster or defeat the nomination. The result, we hope, will be a justice that can help restrain the court’s conservative activists.

Activism on the court was evident in January, when a  5-4 Supreme Court majority struck down rules restraining the role of corporate money in election campaigns. Stevens, in a minority opinion he read from the bench, criticized the majority for forsaking judicial restraint and using a narrow case to overturn well-established law.

“Essentially five justices were unhappy with the limited nature of the case before us, so they changed the case to give themselves an opportunity to change the law,” he wrote.

Republican senators are already warning that they will vigorously fight any judge they consider too far to the left. Whoever is nominated can expect to provoke the usual routine of scrutiny, controversy and outrage from an array of politically oriented critics.

In the end, the Senate has proved willing to accept a president’s nominee, so long as his or her legal views do not stray far from the mainstream. Liberals should recognize this reality, and the fact that moderates ”“ like Stevens ”“ have played a key role in protecting our rights.