Hillary Clinton is facing one sure roadblock on her way to a clean sweep through the South Dakota and Montana primaries on June 3rd. That state is North Carolina, where Clinton has trailed Barack Obama by double digits in six of nine nonpartisan polls conducted since her wins in Ohio and Texas.

Clinton is expected (at least, by Smart Politics) to post big wins in Pennsylvania (April 22nd), Indiana (May 6th), West Virginia (May 13th), and, of interest to this entry, Kentucky (May 20th).

While Kentucky is located a tad northwest of North Carolina, these southern states offer a simple, but persuasive explanation as to why Clinton will trounce Obama in the former, but is struggling to get within single digits in the latter. While the data below from the U.S. Census is not broken down by partisanship, it is evident which state generally caters to each candidate’s base of support.

To begin with, Kentucky is a more rural state, a positive demographic for Clinton (in primaries, not caucuses). In the Bluegrass State there are 101.7 persons per square mile, compared to 165.2 in North Carolina.

Obama performs particularly strong among the wealthier (Democratic) populations. Kentucky, however, is a poorer state with a median household income of nearly $4,000 less ($37,046) than in North Carolina ($40,863). The percentage of residents who live below the poverty level is also notably higher in Kentucky (16.3 percent) than in North Carolina (13.8 percent).

Obama also performs very well among more educated populations, and the percentage of residents who have earned a high school diploma is 4 points higher in North Carolina (78.1 percent) than in Kentucky (74.1 percent). Likewise, the percentage of residents who have received a Bachelor’s degree is much higher in North Carolina (22.5 percent) than in Kentucky (17.1 percent).

Finally, and most importantly, North Carolina is home to approximately three times as many blacks (21.7 percent) as Kentucky (7.5 percent), based on the percentage of each state’s population. Obama is drawing support of 80 to 90 percent of blacks in most primaries.

The result: Obama boasts double digit leads among likely voters in North Carolina in recent polls by InsiderAdvantage (15 points) and LA Times / Bloomberg (13 points). SurveyUSA, meanwhile, has just staked Clinton to a 36-point lead in Kentucky, 62 to 26 percent.