I had always assumed the Whig overperformance in the Deep South that year came mainly from future Unionist strongholds. But a look at the county map shows otherwise; the areas were slavery was less prominent held out for Van Buren; while the present day Black Belt of Georgia, Alabama, and Mississippi where slavery was most common mostly voted for Harrison.
I can't wrap my head around it. I know the Whigs were hardly an abolitionist party, but surely most slaveowners knew that Democrats were more supportive of the "peculiar institution" than Whigs. In turn, why did Van Buren do so well in areas outside the Black Belt?
That depends on which Democrats and which Whigs. Ultimately Whigs were the party of the business elite and Dems of the working person and this didn't change just because of the Mason-Dixon Line.
Naturally then, it makes sense that Southern Whigs would be more supported by the plantation class than that of Democrats.
And of course, Van Buren was a Northern Democrat, and not necessarily of the "dough-face" variety like Pierce or Buchanan.
Even in 1836, Van Buren arguably profited off a vote-split in the Whigs as he barely won LA and MS and still lost TN and GA to Hugh White. Only AL and AR were convincing wins. Ergo, he was already vulnerable there when vying for re-election, even in good times.
EDIT: And NCY beat me to it, and put it even better!
