The Potter Stewart Standard

Kerry's suggesting that the right kind of judge is one whose political opinions aren't detectable in his rulings. But in the context of jurisprudence, where "liberal" and "conservative" tend to reflect different interpretive stances rather than policy views, I just don't buy that it's possible. Does a judge make every effort to defer to Congress in the absence of an unambiguous prohibition on the kind of law in question, or does he read terms like "equal protection" or "establishment" more broadly? How can differences like that not be apparent in a decision?