4. New Justices Can't Change the Court
In the short term, for this reason, it is unlikely that Obama's choice will move the court's ideological needle. But over the longer run, his pick could matter a great deal. If recent history is any guide, Obama's nominee will serve on the court for 20 years or more and thus outlast most of the other Justices. A pick who might seem relatively unimportant at the outset (like President Nixon's selection of William Rehnquist) might well become very important and influential over time, even becoming the Chief Justice, as Rehnquist did. A long run by a now young appointee could be especially pivotal on a court like the current one, where the ideological split is 5-4 on almost every controversial issue.
In sum, no matter what tales we tell ourselves, we will not be able to escape the inconvenient truths that judicial politics is hugely divisive, hugely important and, at the moment, tragically predictable, as our Supreme Court will continue to mirror our most divided selves.