In an essay that appeared in The Washington Post over the weekend, Rutgers University historian David Greenberg suggests that Barack Obama's popularity with white voters hurts him with African-Americans.

"Some pundits scratched their heads when Obama was trailing Clinton among black voters. (He's now pulled even or ahead.) But it made perfect sense," Greenberg writes. "Clinton had a track record of working for African Americans' interests. Obama was not just skirting controversies such as the "Jena Six" -- the black Louisiana teenagers punished disproportionately last year for their role in a racial fracas -- but was aiming his appeals squarely at the white Iowans who he knew could make him the front-runner."

K.C. Johnson disagrees. Writing at the History News Network's Cliopatria blog, Johnson explains that the chief reason Obama lagged in support among black voters was because they did not believe an African-American could win. 

"After Obama’s win in Iowa, which suggested he could be electable, his support among black voters surged -- not only in South Carolina, but even in Clinton’s home state, where a Daily News poll out today showed Obama leading among New York black voters," Johnson writes. "In this respect, the timing of Greenberg’s column turned out to be unfortunate."