His claims about those states don't stand up very well to the math.
To begin with, African-Americans in Mississippi and Georgia already come close to voting their percentage of the population. The suggested gains, while they may be welcome, would not be large enough to turn the tide in these red states.
In the 2004 presidential election, blacks made up 34 percent of the voters who turned out in Mississippi, where they comprise 37 percent of the population. The numbers are similar in Georgia. In South Carolina, blacks actually made up a slightly larger portion of Election Day voters than they did of the population.
Still, the Democratic candidate, John Kerry, went down to defeat in those states.
Enter Obama, who says his African-American heritage changes the game in 2008. What if blacks did vote their percentage of the population in the states he mentions?
Say he gets every black Mississippi vote that Kerry got in 2004. (about 352,500). Then say he gets the Mississippi white voters who supported Kerry (105,200). Then give him all of the 72,600 black voters who would turn out if Mississippi blacks voted their percentage of the population in 2008.
That's about 530,300 total votes for Obama — still short of the 685,000 Mississippi votes that went to George W. Bush in 2004.
In sum, he falls short by more than 150,000 votes in Mississippi, about 300,000 votes in Georgia and more than 200,000 votes in South Carolina - even using the most favorable estimates.
We did the same analysis on the rest of the Southern states. The math works out the same everywhere but in Florida, where the margin between the parties is so close that an extra 400,000 black voters — all supporting Obama — might buy him a very narrow victory.