“Do I think he’s a civil rights leader? No,” said Al Sharpton, who has become close to Obama in part because they are of the same post-movement generation. “I think he’d be the first person to tell you that.”

So when Obama settles into King’s footsteps at the base of the Lincoln Memorial on Wednesday, half a century after the 1963 March on Washington, black leaders will be listening not for the inspirational rhetoric of a civil rights icon but for the substance of a president.

“Those are two different roles,” said Jesse Jackson, who has had his differences with Obama. “What we needed from Dr. King was motivation and vision. What we need from the president is appropriation and legislation.”

Rep. John Lewis (D-GA) — who was the youngest speaker during the March on Washington in 1963 — delivered a passionate address about the importance of protecting voting rights at the steps of the Lincoln Memorial fifty years later, as thousands gathered to celebrate the anniversary of the historic event on Saturday.

“When I stood here 50 years ago, I said one man, one vote is the African cry. It is ours, too. it must be ours,” he began, before connecting the demands of 1963 to today’s struggles. “Almost 50 years ago, I gave a little blood on that bridge in Selma, Alabama, for the right to vote. I am not going to stand by and let the Supreme Court take the right to vote away from us!”

Eric Holder, the nation’s first black attorney general, said he would not be in office, nor would Barack Obama be president, without those who marched.

“They marched in spite of animosity, oppression and brutality because they believed in the greatness of what this nation could become and despaired of the founding promises not kept,” Holder said.

Holder mentioned gays and Latinos, women and the disabled as those who had yet to fully realize Martin Luther King Jr.’s dream. Others in the crowd advocated organized labor, voting rights, revamping immigration policies and access to local post offices.

“The task is not done, the journey is not complete,” [Martin Luther King III] said. “The vision preached by my father a half-century ago was that his four little children would no longer live in a nation where they would judged by the color of their skin but by the content of their character.”

“However, sadly, the tears of Trayvon Martin’s mother and father remind us that, far too frequently, the color of one’s skin remains a license to profile, to arrest and to even murder with no regard for the content of one’s character,” he said, calling for “stand your ground” self-defense laws to be repealed in states where they have been enacted.

Referencing King’s quote in his “I Have A Dream” speech about America giving people “a check that has come back marked ‘insufficient funds,’” Sharpton called for action to make lawmakers take notice about the financial disparity in the United States.

“We’ve re-deposited the check. Well, guess what? It bounced again. But this time it was marked stop payment,” he said, addressing Congress with his words. “We’re going to make you make the check good or we’re going to close down the bank.”

Kevin Moore, 47, said he came with about 60 people from Columbus, Ohio, to urge unity in Congress.

“I figure is we come out and unite and show we’re serious. There’s gonna be change,” he said, a bright yellow “Support Trayvon’s Law” in his hands.

Mr. Moore said he was holding his sign, made by the NAACP, because the slaying of Florida teenager Trayvon Martin “hit close to home.”

“It could have been our child,” he said.