Steve Ansolabehere, Nate Persily, and Charles Stewart have written this article for the Harvard Law Review Forum.  Here is the conclusion:

Reasonable people can disagree about the relevance of the 2012 election or even racially polarized voting patterns to the constitutionality of the coverage formula for section 5 of the Voting Rights Act. Indeed, we view our findings more as a response to the notion that the election and reelection of an African American President settles the constitutional question in favor of the VRA’s detractors. If anything, the opposite is true. To be sure, the coverage formula does not capture every racially polarized jurisdiction, nor does every county covered by section 5 outrank every noncovered county on this score. However, the stark race-based differences in voting patterns between the covered and noncovered jurisdictions taken as a whole demonstrate the coverage formula’s continuing relevance.

In particular, for those looking for a way to distinguish the covered jurisdictions from the noncovered jurisdictions, and to do so without running afoul of the “elephant whistle” problem, differential rates of racially polarized voting provide an ideal metric. There can be no doubt that the covered jurisdictions differ, as a group, from the noncovered jurisdictions in their rates of racially polarized voting. There can also be no doubt that voting in the covered jurisdictions as a whole is becoming more, not less, polarized over time.

This is a must-read, careful analysis.  The question, which I first posed in 2005, is whether differences in racially polarized voting are of constitutional significance to save section 5 of the Act for the swing Justice(s) on the current Supreme Court.  On that question, we  likely will have to wait until the end of June.