Usurprisingly, Barack Obama won yesterday's presidential primary in Mississippi, by a healthy 61-37 margin. The win will glean him six net pledged delegates, and add to his cumulative popular vote lead (potentially a very big deal) by nearly 100,000.

Much is being made today of the racial breakdown in the MS vote. Nobody should have been surprised. MS, like SC and AL, is a state where racial polarization is a fundamental political reality. Obama has done relatively well among white voters in those southern states (GA and VA) where biracial coalitions are far more common. I suspect he'll do pretty well among white voters in NC as well.

A couple of other exit poll findings are of interest. Despite the racial bent of the vote, age was also a big factor, with Obama's success declining systematically up the age ladder. Fully 12 percent of the primary turnout was among self-identified Republicans, who went for HRC by more than a three-to-one margin; this undoubtedly added to the racial polarization of the overall results.

Now it's on to the long, hard slog towards Pennsylvania on April 22.