A liberal supreme court justice will retire and be replaced by a liberal supreme court justice. Breaking news there.
That's not what liberals want. They're looking for what happened in 2005, when Sandra Day O'Connor unexpectedly stepped down (to care for her sick husband, I think) and President Bush replaced her with Samuel Alito.
Bush replaced a liberal with a conservative, giving the Supreme Court, what many liberals believe to be, a "far right" high court.
That's one of the reasons, BTW, why some gay activists don't want their buddies to bring a lawsuit about DOMA to the high court, fearing that a loss now would set them back for decades.
Back to Stevens, he's often seen as a swing judge. I remember in the two cases involving displays of the Ten Commandments on state capitals (one in Texas, the ohter in Kentucky, if memory serves me correctly). The court ruled against the Kentucky case, ordering that the monument had to be moved but ruled IN FAVOR of letting the one in Texas stay put. Stevens was the deciding judge.