When Martin Luther King, Jr., shared his dream from the steps of the Lincoln Memorial in 1963, the president of the United States was not there to bear witness.
John F. Kennedy was skeptical of the March on Washington, choosing to watch the event on TV from inside the White House several blocks away. He later clashed with King over the urgency for legislation to match the march's message of "jobs and freedom."
Fifty years later, amid renewed calls for urgency to address racial disparities in America, the nation's first black president Barack Obama will add his voice to the campaign. He is the marquee speaker during Wednesday's anniversary at the same steps where King stood.
Watch the 50th Anniversary of MLK's "I Have a Dream" speech LIVE Wednesday 11:30 a.m. ET with Social Soundtracker.
President Obama "is the Jackie Robinson of the highest political circles, the highest practice of politics in American life," said Randall Kennedy, a Harvard University law professor and black historian who clerked for Supreme Court Justice Thurgood Marshall. "The fact that he won [the presidency]…is his great contribution to the civil rights movement, and it's a huge contribution."
Organizers say Obama's historic achievement will be celebrated as a fulfillment of part of King's vision of equality, coming five years to the day when Obama broke the race barrier in presidential politics, accepting the Democratic nomination in Denver.
Yet Obama's emerging legacy on the advancement of King's broader vision is more complicated, some black leaders concede, a mixed bag of achievements that has at times fallen short of the super-human expectations many African-Americans had when he first took office.
Only one in four African-Americans say the situation of black people has improved during Obama's tenure, according to a new Pew Research Center poll. One in five said things have gotten worse. Half of blacks say things are about the same now compared with five years ago, a view shared by as many whites surveyed in the poll.
The findings underscore the stubbornness of socio-economic disparities that have frustrated the African-American community and at times thwarted Obama's attempts to address it.
"What's disturbing is to see that even with a black president -- not necessarily his fault -- but there's still so many things that need to change in this country, we still have a long way to go," said Lynn French, a Washington, D.C., native who helped organize the 1963 march.
Unemployment among blacks remains in the double-digits, at 12.6 percent in July, nearly double the rate of whites. The median household income for a typical black family is just 60 percent that of whites – a gap that has grown since 2009. Nearly one in three blacks lived in poverty in 2011, almost double the national average.
While many community leaders recognize these problems as bigger than Obama alone can solve, there is a sense in some corners that he, like Kennedy, has failed to demonstrate a sufficient sense of urgency.
"What allows President Obama to so readily address this 50th anniversary celebration is the fact that King is now a dead martyr," wrote prominent black commentator Tavis Smiley in a recent op-ed for USA Today. "Otherwise, like Kennedy, Obama might also be mired in anguished soul-searching about whether to share the podium with a man who would undoubtedly be espousing uncomfortable and inconvenient truths."
Other notable black critics question why Obama has not spoken more regularly on race relations, pointing to the only handful of times he has directly addressed the issue and even then seemingly reluctantly. After George Zimmerman was acquitted in the killing of Florida teen Trayvon Martin, Obama did not speak on-camera about the case or ensuing national demonstrations until six days later.
Some skeptics of Obama's commitment to King's dream, including Princeton professor Cornel West, accuse the president of failing to pursue an African-American specific legislative agenda.
Yet, many blacks say the grumblings about Obama, while not insignificant, are on the margins. The president retains overwhelming approval among blacks – 86 percent in the latest Gallup poll, compared with just 36 percent among whites – and he won more than 90 percent of the black vote in two consecutive elections.
"It is important that the president be scrutinized and constructively criticized," said Hillary O. Shelton, director of the NAACP Washington bureau and the advocacy group's chief legislative lobbyist.
"We are not delusional. But it's a narrow focus to only look at the data and not recognize that African-Americans are sophisticated enough to recognize what the reality is of changing that condition," he said. "There's a lot to be said for what President Obama has brought."