President Obama greets supporters after a rally at Chicago State University on Oct. 19 in Chicago. Obama attended the event to campaign for Illinois Governor Pat Quinn, who is running for reelection. (Brendan Smialowski/AFP/Getty Images)

President Obama has been busy courting African American voters on black radio, and Democrats have been running ads in black newspapers that urge voters to "Get His Back."

But, as I've written before, it's unlikely to be enough in key states because of the declining standing of Democrats among white voters. And a new report by the Joint Center for Political and Economic Studies drives home that point.

The chart (click it to make it bigger) is bad news across the board for Democrats in Southern states. It shows that the white vote that candidates like Sen. Mark Pryor (D-Ark.) are likely to get on Election Day is probably not enough to get to a majority, even with high black turnout. A state like Arkansas is similar to Kentucky with a smaller population of black voters, so getting white support is especially crucial. In both of those states, black voter turnout was below 40 percent in 2010.

According to the study, the magic number for Democrats is much closer to 40 percent of the white vote, in combination with a strong black turnout. At that mark, Democrats would likely have a big enough multiracial coalition to put together a win. But the multiracial part is the key.

In Louisiana, Sen. Mary Landrieu (D) is getting only 22 percent of the white vote, according to October polls. In 2008, with a bigger electorate overall, she got 33 percent of the white vote. Democrats in Georgia are only getting a quarter of that vote. Those races will likely go to a run-off, and that's probably a steeper hill for Democrats. Sen. Kay Hagan (D-N.C.), meanwhile, has a third-party candidate mixing up the electorate enough so that she could possibly win without an outright majority of voters.

Yes, the black vote is very important, which is why Democrats have mounted a multimillion-dollar voter outreach campaign. But a big takeaway from this campaign will be how well Democrats sell their message to white Southerners.