The evening before the launch, Thomas Paine, who was the administrator of NASA, met with the S.C.L.C. protesters. Although Abernathy had been warned they would be turned away, the caravan was invited in. About 40 of them, mostly children, toured the grounds. And although Paine and Abernathy had a terse meeting, the next day, 10 of the protesters were seated in the V.I.P. section of the launch, among senators, generals and Johnson. They looked up to watch America’s rocket penetrate the sky.

Abernathy described being captivated by the moment along with the rest of the nation. He’d told Paine the previous evening, that he would be praying for the astronauts. And Paine, in turn, had expressed his care for the plight of poor Americans. These expressions of mutual respect in the midst of a historic moment, however, did not smooth over the conflict. They exposed the essential tension at the root of the nation. America’s ambition persistently stopped short of the equality creed, and yet it seemed to always demand a self-effacing patriotism from even the most vulnerable, including the poor folks who marched with Abernathy on Cape Kennedy.

And this is among the myriad reasons we cannot tell history as a matter of simple forward progress. In the calendar of landmark events, 1969 is an important year. It is the year of Woodstock and Stonewall. The Women’s Movement was amping up, and the Antiwar movement was in full throttle. In retrospect, it is easy to see the heroism of the moment. But we often neglect the excruciating wrangling in the thick of it.

The day after Neil Armstrong and Buzz Aldrin set their feet on the moon, King’s brother, A.D., was found dead. He had drowned in his pool despite being a skilled swimmer. By many accounts, depression and alcohol had clouded his life since his brother’s death, and the pressures of the movement weighed heavily on his heart. In those heady and by many measures, victorious times, hearts broke, and so did people.

But for some of the others, history marched forward. Andrew Young, one of the protesters, went on to become the mayor of Atlanta. Another, Hosea Williams, would create “Hosea Feed the Hungry and Homeless,” an international aid and social services organization. And after former President Richard Nixon signed the District of Columbia Delegate Act, Walter Fauntroy was elected as Washington’s first delegate to Congress.

Years later, though, Abernathy’s legacy would be sullied by virtue of a salacious memoir about his escapades with King, and it was hard not to see that as a break of sorts, too. History is messy, and human vulnerability collides with the most starry moments. Abernathy’s headstone reads, “I tried.”