All eight Democratic hopefuls and a lone Republican candidate, Colorado Rep. Tom Tancredo, addressed the NAACP convention. The Democrats focused their criticism on the administration's record on race relations.
"We know we have more work to do when Scooter Libby gets no prison time and a, who hadn't even committed a felony, gets 10 years in prison," Obama said to loud cheers.
Aides said Obama was referring to Genarlow Wilson, a Georgia man serving a 10-year prison sentence for having consensual oral sex with a 15-year-old girl when he was 17. A judge last month ordered Wilson to be freed, but prosecutors are blocking the order.
Libby, the former chief of staff to Vice President Dick Cheney, was convicted of lying and obstruction of justice in the CIA-leak case. He received a 30-month prison sentence, which Bush commuted last week.
In their bid to woo black voters, a key party constituency, all the Democratic hopefuls shared the stage at the forum devoted to racial issues.
Front-runner Hillary Rodham Clinton predicted the forum would cover more issues of importance to the black community than the administration had in six years.
"We have a president who does not see what you and I see. ... With your hard work, we will render the people that you and I see visible once again," the New York senator said. She cited "The Invisible Man," Ralph Ellison's famed novel of black alienation.
John Edwards touted his commitment to fighting poverty, calling it "the cause of my life." Edwards will launch a tour Monday in New Orleans to spotlight the millions living in poverty.
"We want America to see the other America," Edwards said. "That seems to be forgotten."
While all the contenders were warmly received as they took their place onstage, Obama received a boisterous, sustained ovation.
Tancredo said he accepted the invitation to speak because his message is for all Americans. A vociferous foe of illegal immigration, Tancredo said the wages of black workers suffer because of illegal workers.