With four justices in their 70s, odds are good that whoever wins in November will fill at least one Supreme Court seat. The next justice could dramatically alter the direction of a court split between conservatives and liberals.
One new face could mean a sea change in how millions get health care, shape gay rights and much more.
Obama already has put his stamp on the court by selecting liberal-leaning Justices Elena Kagan and Sonia Sotomayor, 50-somethings who could serve a quarter-century or more. Romney has promised to name justices in the mold of the court's conservatives.
Since the New Deal, Supreme Court decisions have made huge differences in American lives, from rulings to uphold Social Security, minimum wage laws and other Depression-era reforms to ringing endorsements of equal rights. Big decisions on health care, gun rights and abortion have turned on 5-4 votes.