Imagine a color test where we had to describe colors on a chart while wearing goggles with either blue or red lenses. The binary red vs. blue goggles would influence our descriptions.
The analogy to law is that if our only lens choice for reading Supreme Court decisions is party politics, red or blue, we miss the true colors.
Consider this weeks' decision by the Supreme Court (Caetano v. Mass.) saying the Second Amendment covers stun guns. The decision was unanimous--eight to zero even in the absence of Justice Scalia ( the Court's Second Amendment former leader). Red/blue goggles would have predicted a 4-4 split...wrongly.
Constitutional decision-making runs by a different set of principles than Blue vs. Red Goggles. (So it is that Bush appointee Chief Justice Roberts could cast the deciding vote in favor of Obamacare.) Life appointees to the Court enter the Constitutional halls of the independent judiciary and can surprise those wearing Blue vs. Red Goggles.
The current nomination debate should keep that in mind.