The story is in the Columbia State newspaper, which reports that during a visit to South Carolina Jackson criticized Obama's "tepid response" to the case of the so-called "Jena Six," a group of black students arrested for attempted-murder in Jena, Louisiana. (More on that here.) Obama's campaign, as well as Hillary Clinton's, released a statement about the case, with Obama's stating that "when nooses are being hung in high schools in the 21st century, it's a tragedy."
"Jena is a defining moment, just like Selma was a defining moment," the newspaper quotes Jackson saying.
But the paper also points out that Jackson later said he did not recall making the "acting like he's white" statement. He does, however, maintain that Obama is not taking advantage of his national profile to bring more attention to cases like that of the "Jena Six." Jackson, a former presidential candidate himself, endorsed Obama six months ago.
Update: The Obama campaign sent CBS news the following statement from Jackson: "I reaffirm my commitment to vote for Sen. Barack Obama. He has remarkably transcended race, however the impact of Katrina and Jena makes America's unresolved moral dilemma of race unavoidable. I think Jena is another defining moment of the issue of race and the criminal justice system. This issue requires direct and bold leadership. I commend Sen. Obama for speaking out and demanding fairness on this defining issue. Any attempt to dilute my support for Sen. Obama will not succeed."