They hit the notes, but do they know the song?

SUMTER, S.C. -- Who's faking it, and who's for real?

That was the question Barack Obama put to a mostly black audience at an NAACP dinner earlier tonight in Sumter, a city in the South Carolina Midlands. "I've been there in the trenches," Obama told 800 people packed into the Morris College gymnasium, his booming voice distorting the PA system.

He continued, "Can I be honest for a second? We've been hearing the same thing from Democratic candidates for president for the last 30 years."

Obama did not single out rival Hillary Clinton, who has also addressed NAACP events and who is competing mightily with Obama for black voters in South Carolina. But the reference seemed clear when he said, "Everybody knows all the right notes to hit, especially when they're speaking before the NAACP." Then he inserted a white-candidates-can't-clap joke about his rivals' rhythm -- or lack thereof: "They might not clap on time." The crowd got it.

But Obama's point was a serious one. "The question is not who says the right words," he said, "but who has the judgment and the courage to act on those words, even when it's hard, even when it's inconvenient."

Obama, of course, is trying to persuade voters that he's the one with that courage and judgment. And he knows that black voters, who make up a significant chunk of the Democratic electorate in South Carolina, must believe him.

Earlier in the day, Obama held a rally in front of the courthouse in nearby Clarendon County, the site of one of the original cases that led to the landmark Brown vs. Board of Education Supreme Court decision integrating American schools. The work of ensuring equality in education is far from finished, he said. "We need to start treating these kids like our kids," he said.