President Barack Obama, accompanied by the first lady and two former Democratic presidents, walked down the stone steps past a cast iron bell from a Birmingham, Ala., church where a bombing killed four black girls in September 1963.
Taking the lectern, the nation's first African-American president paid homage to King's legacy, saying that "because they kept marching, America changed." But Obama warned that the struggle for equality is not yet complete, adding that "the arc of the moral universe may bend toward justice, but it doesn't bend on its own."
"To secure the gains this country has made requires constant vigilance, not complacency," Obama said. He cited as setbacks the Supreme Court's decision in June to strike key provisions of the 1965 Voting Rights Act and the high rates of African-American incarceration.
At a time of slow economic recovery, Obama emphasized that while his own presence in the White House symbolized how far the nation has moved on racial tolerance, such victories threatened to obscure the other major goal of the 1963 rally: economic justice.
The nation's unemployment rate for African-Americans remains far higher than for other racial groups, and Obama, concerned by a growing income gap, has pressed Congress to invest in infrastructure, education and research at a time when Republicans are championing deep budget cuts to rein in the deficit.
Seeking, perhaps, to help revive his flagging domestic policy agenda ahead of a September budget fight, the president said the country faced a critical choice, as it did in 1963, between stalemate and progress.
"We can continue down our current path in which the gears of this great democracy grind to a halt and our children accept a life of lower expectations," Obama said, "where politics is a zero-sum game, where a few do very well while struggling families of every race fight over a shrinking economic pie. That's one path."
Or, he continued, "we can have the courage to change. The March on Washington teaches us that we are not trapped by the mistakes of history, that we are masters of our fate. But it also teaches us that the promise of this nation will only be kept when we work together. We'll have to reignite the embers of empathy and fellow feeling, the coalition of conscience that found expression in this place 50 years ago."
It was a day of remembrance and unity, but the absence of any Republican speakers among the dozens of politicians and activists who addressed the crowd was notable at a time of deep partisan divide in Washington.
Several GOP officials, including House Speaker John Boehner, R-Ohio, said they had been invited but had declined after participating in a congressional ceremony marking the anniversary leading up to the march.
At 3 p.m., the time King gave his famous "I Have a Dream" address five decades ago, descendents of King rang the bell, and church bells across the nation chimed three times. A gospel singer began to sing, as Obama, forgoing an umbrella despite a persistent drizzle, prepared to make his address in the shadow of his famous forebear.
Before Obama's appearance, the panoply of speakers traced how much progress the United States has made over five decades.
"This moment in history is a long time coming, but the change has come," said Rep. John Lewis, D-Ga., the last living speaker from the 1963 rally.
But, as other speakers did, Lewis, who marched along with King and other civil rights leaders, warned that the progress should not be mistaken for full equality at a time when African-Americans face higher unemployment rates.
"We've come a great distance in this country in the 50 years, but we still have a great distance to go before we fulfill the dream of Martin Luther King Jr.," Lewis said.
Former President Jimmy Carter, after praising the legacy of King, whom he called perhaps the nation's most important leader, recited a list of ongoing challenges: the Supreme Court's ruling in June that struck down key provisions of the 1965 Voting Rights Act, high unemployment in the black community, lenient gun- control laws and a lack of voting rights in the District of Columbia.
"I think we know how Dr. King would have decried" those problems, Carter said.
Former President Bill Clinton was even more forceful about what he views as the misplaced priorities of the country.
"A great democracy does not make it harder to vote than to buy an assault weapon," Clinton said. But he added that the public should not complain about the political gridlock in Washington.
"We don't face beatings and lynchings and shootings because of our political beliefs anymore," he said. "Martin Luther King Jr. did not live and die to hear people complain about political gridlock. It's time to stop complaining and start putting our shoulders together against the stubborn gates holding America back."
Some celebrants set off on the actual path of the 250,000 who marched on Aug. 28, 1963, retracing the footfalls that helped begin a cultural earthquake and eventually shook apart the bulwarks of legal discrimination against African-Americans. There were long lines at the security checkpoints, and some people were treated for heated-related conditions by medical personnel.
Umbrellas and ponchos took the place of mid-century fedoras and skinny ties. But some still talked of recapturing the mood of the March on Washington for Jobs and Freedom, an event that has been described as a day of euphoria amid the chaos and clashes of the 1960s. And they spoke of reclaiming the unfinished business of the movement at a time when African-Americans still lag far behind whites on economic and educational attainment.
"Fifty years ago we had to convince the president to let us come. Today, the president is coming to us," exulted Del. Eleanor Holmes Norton, the District's non-voting member of Congress, as the crowd grew around her. Back in 1963, she was one of the young staffers organizing the march.
For marcher Tara Childs, the number of black faces she sees in unemployment offices tells her King's dream is far from realized.
"The issues they were marching for in 1963 were economic," said Childs, 35, co-chair of Young and Powerful, a national group of young professionals, as she headed toward the Mall. "When I see the footage, I am moved, because I feel we are still combating the same issues. The unemployment rate is still ... disproportionately high among African- Americans."
Others were ready to celebrate five decades of racial progress that means many young people are more familiar with sharing playgrounds, classrooms and bedrooms with members of other races than with the segregation and resistance to change of King's era.
For David Figari, the moment seemed perfect to cement his own relations across racial lines. On the steps of the Georgetown University Law Center, just before setting out on a 1.7-mile march to the Lincoln Memorial, Figari, who is white, asked Jessica Jones, who is black, to marry him. They are both 25-year-olds from Tampa, Fla.
He knelt on the steps in front of his girlfriend and held out a ring. She said yes, and their fellow marchers exploded in cheers.
Figari had planned to propose in November, when the couple would be on a ski trip together. But he changed his plans when they decided to join the commemoration of the 1963 march.
"I figured this would be a little more deep," he said. "I think our relationship brings the whole idea of the march to fruition."
At an interfaith service Wednesday morning at Shiloh Baptist Church in Northwest Washington, faith leaders reprised King's message in the context of their own traditions, from Sikh to Southern Baptist.
"Hate cannot drive out hate, only love can do that," said Imam Mohamed Magid, president of the Islamic Society of North America. Magid recalled how he leaned on King's memory in the period of violence against Muslims after the Sept. 11, 2001, terrorist attacks. "It brought tears to my eyes. His message of diversity is that God created all people. That we can walk together on the path of peace"
King's legacy has formed a part of the basic curriculum at her children's school, said Rabbi Julie Schonfield, executive vice president of the Rabbinical Assembly. "The first history they are taught is the history of the civil rights movement."
The day was the second major commemoration of the march this week, causing some confusion on social media by those seeking the official remembrance. The duplication reflected, in some ways, generational divisions in the civil rights community that have widened in a half century.
An event Saturday that also brought thousands to the Mall was organized by the National Action Network, a group headed by the Rev. Al Sharpton. Wednesday's gathering featured involvement of the NAACP and other legacy civil rights groups. Both had participation from members of the King family.
Still, the lines at security checkpoints were long by noon Wednesday, despite hot muggy weather on a workday. That was an oppressive contrast to the splendid sunshine of Saturday's event and less forgiving than the glorious summer day that greeted marchers 50 years ago. On Saturday, umbrellas were a shield against the sun. On Wednesday they were protection against the rain.
"I think it's going to clear up," said Aijalon McMillian, 20, of New Brunswick, N.J., as his friend opened an umbrella in the sprinkling rain. "I think the sun's going to come out."
It wasn't just rosy nostalgia that had veteran marchers remembering the day of the original gathering as just about ideal.
"By Washington standards, August 28, 1963, was an extremely pleasant summer day here, with temperatures ranging between 63 and 83 degrees, no rain, and dew points in the comfortable 50s," said Don Lipman of The Post's Capital Weather Gang.
Heavy skies or not, many came to note their own history with Jim Crow and, in some cases, the personal outrages that brought them to Washington 50 years ago.
Nannie Blakeney remembers when her grandmother was a housekeeper for a white family. Blakeney would play with the family's children, but wasn't permitted to sit down with them for lunch.
"I wanted to eat with the little girl, and they said I had to eat in the kitchen," she said. "I kept asking my grandmother, 'Why? Why?' She said because if you don't they'll beat you."
Blakeney was 13 when she made the trip from Virginia to the March on Washington in 1963. She heard King talk about his dream and " thought it might come true," she said. "We've come a long way. I have mixed-race grandchildren now."
Others on the Mall were born long after the laws that assigned bus seats and lunch spots based on the color of a customer's skin. But the young brought their own concerns Wednesday, from scarce jobs to rampant violence.
Antoine Pendleton, 23, said both were on his mind on this 50th anniversary.
"I'm a black male trying to succeed out here," said Pendleton, a recent graduate of Taney Institute, a historically black college, who works at a home in Pittsburgh for people with severe disabilities. "Get the guns off the street. I'm trying to make it to the 75th anniversary."
If the marchers of 1963 would have been agog at the idea of black president five decades later, they might have been even more stunned by the hyper-merchandizing that surrounds him. The vendors were out in force Wednesday, with $10 Obama piggy banks, $3 first-family tote bags and much more.
And there was Obama himself. Two of him, if you count the cardboard cutout of the president that Catherine Nanfuka carried over her shoulder.
On Wednesday, she could barely move 10 feet without being approached by someone who asked to be photographed the life-size but flat president.
"It makes me so happy," Nanfuka said. "You should see the reaction. People say 'I can't believe it's free to take a picture. Here, take a dollar!' But, no, it's free."
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