Although the tent was crowded with living history — President Obama, Rep. John Lewis, Colin Powell, Steve Case, Al Sharpton and Laura Bush — the speakers at the groundbreaking of the Smithsonian African American museum emphasized the future.

And not just the impact of having the National Museum of African American History and Culture on the Mall. Not only the building. But also the learning legacy it will give the children of the coming generations.

“The time will come when few people remember drinking from a ‘colored’ water fountain or boarding a segregated bus, or hearing in person Dr. King’s voice boom down from the Lincoln Memorial,” said Obama, explaining what the new museum will teach. He spoke about his family’s future and how the museum will intersect with Americans far away from many essential points of history.

“In moments like this . . . I think about my daughters,” he said. “When our children look at Harriet Tubman’s shawl or Nat Turner’s Bible . . . I don’t want them to be seen as figures somehow larger than life. I want them to see how ordinary Americans could do extraordinary things.”

The groundbreaking Wednesday symbolized a determined step forward to having a presence on the Mall tell the story of the African American experience. The museum, authorized in 2003 by Congress, has been raising money (about $100 million so far) and collecting artifacts (about 20,000 to date) for the building. The museum is expected to cost $500 million and open in 2015.

Dignitaries — including Laura Bush, a member of the museum’s council — moved some sandy earth around with silver shovels.

Speakers at the 90-minute ceremony, attended by 600 invited guests and anchored by actress Phylicia Rashad, stressed that the museum will not only tell the African American story, but also an American story.

“We must tell the story, the whole story of the last 400 years, without anger or apology,’’ said Lewis (D-Ga.), who introduced the legislation in the House to create the museum. Former senator Sam Brownback (R), now the governor of Kansas, said the museum would have a factual and emotional sweep. “The African American people have experienced the worst of our shortcomings,” he said. Yet “America’s grandchildren,” Brownback said, would see “the triumph of the African American people.’”

The museum’s journey and the role of black life in Washington was underscored by Bush, who told of the slaves who helped build the White House and the U.S. Capitol and how “Lincoln was horrified by the sight of the slave pens” within view of the latter. She described how President Lyndon Johnson fought for civil rights legislation. Of the museum, she said, she was “glad it will stand next to the monument to our first president, George Washington, who freed his slaves in his will.”

The program previewed the rhetorical styles and the music legacies that will most likely be celebrated in the museum. Mezzo-soprano Denyce Graves, a native Washingtonian, sang the national anthem. Thomas Hampson performed from the William Grant Still and Aaron Copland songbooks. Jason Moran, a jazz pianist, played Duke Ellington. Several choirs joined Graves and Hampson on a finale of the traditional “Lift Every Voice and Sing.”

The Rev. Calvin O. Butts III, pastor of the historic Abyssinian Baptist Church in New York, combined a number of poems and hymns to point out that success is visible, but not complete, with the election of Obama, the establishment of the Martin Luther King Jr. Memorial and now the museum. D.C. Mayor Vincent C. Gray echoed that thought. The museum, he said, will be a “tangible manifestation of Dr. King’s dream.”

The museum will not erase the tragedies and struggles that are part of the African American story. The Smithsonian itself is guilty of both racism and contrition, said Richard Kurin, the institution’s undersecretary for history, art and culture: Joseph Henry, an early Smithsonian secretary, refused to let Frederick Douglass speak at a series on abolition, he said, and during the Poor People’s Campaign of 1968, some told the Smithsonian to close its doors to the predominantly black people camped on the Mall. Dillon Ripley, then-secretary, balked at the suggestion and kept the museum open late. “Frederick Douglass’s words will certainly be heard in the rooms of the Smithsonian,” Kurin said.

The museum has been a goal of many generations of black Americans, dating to efforts of Civil War veterans. The narrative within the museum will include the decades of slavery before the Civil War, the history of that conflict, the Reconstruction and Jim Crow eras and the modern civil rights movement. Parts of the museum will be devoted to sports, entertainment, politics and the stories of communities who have been critical to the African American story.

All of that is important, Lewis said, but he said he was looking forward to the museum if only to rest “my tired feet in a cafe.”