Moral indignation at voting patterns is all well and good, but it gets very tiresome very quickly, especially when there's no context or real understanding of the area in question.
I'll now repeat this;
It's ethnic voting as much as it's racist voting. I don't think that Landrieu would do nearly so well there if she didn't have a French surname.
With some fun from the census... 35.2% of people here claimed either French or French Canadian ancestry. The only other large group is "American"... 17.7%. Only about 80% of people actually put down an ancestry; of those about 45% claimed French or French Canadian ancestry.
I can't find the percentage that's still Francophone (and it's a little late at night for it to be worth the bother) but it's definitely over 10%.