President Obama's job in picking a new Supreme Court justice is made tougher by the thin bench left to him after eight years of Republican rule. In fact, too many of the Democrats' best-credentialed judges "would be too old to carve out a meaningful legacy if picked to succeed [Justice John Paul] Stevens," writes Mark Greenbaum. With several relatively youthful Republican members currently serving, he argues the age of Obama’s nominee is a critical factor.