A half century past its zenith, the civil-rights movement has been invested with the kind of moral authority that is derived only from being on the right side of history. We’ve compressed the grand scale of the March on Washington—which took place on August 28, 1963, fifty years ago this coming Wednesday—into succinct quotes, a vine of grainy footage of Martin Luther King, Jr., at the crowded dais, and a dream metaphor whose ubiquity is matched only by its anodyne appeal. There’s an easy certainty afforded to the cause that drew a quarter of a million people to the Washington Mall in August, 1963, not only because of its subsequent success in ending legal segregation and disenfranchisement but also because the fruit of its efforts is currently evident in the office of the Presidency. Yet the massive gathering in Washington, D.C., was driven by the concern that, in the nearly ten years that had passed since the Brown v. Board of Education ruling, the movement had yet to achieve meaningful legislative change—and the uncertainty that it ever would.

Precisely for these reasons, it’s worth remembering the obstacles faced by the men who led the movement, the malevolent skepticism with which they were regarded by not only the forces of segregation but official establishment they were petitioning for redress. And this year, especially, it’s worth remembering that every leader of a civil-rights organization who spoke at the march was, at some point, under surveillance by the federal government.

The aggregated moral will of the civil-rights movement is responsible for the election of an African-American President of the United States—a President who, on Wednesday, will speak at an event at the Lincoln Memorial commemorating the march, and whose tenure coincides with the most expansive capacity for government surveillance this country has ever known. The moral arc of the universe is long, and it bends toward irony.

In early 2007, when his Presidential ambitions were known but not yet significant, Barack Obama addressed a gathering in Selma, Alabama, on the anniversary of the 1965 Bloody Sunday march there. Obama’s name was at that time scarcely familiar to many African-Americans. He was the sole African-American serving in the Senate, yet his connection to the struggle for dignity and equality seemed tenuous, his background exceptional and exotic even to black voters. In his speech—the rhythms of which were more professorial than pastoral—he took pains to sketch the connections between his own background and the odyssey of black America, arguing that he was not an exception to the movement but, rather, the yield of it.

My very existence might not have been possible had it not been for some of the folks here today. I mentioned at the Unity Breakfast that a lot of people been asking, well, you know, your father was from Africa, your mother, she’s a white woman from Kansas. I’m not sure that you have the same experience. And I tried to explain, You don’t understand. You see, my grandfather was a cook to the British in Kenya. Grew up in a small village, and all his life, that’s all he was—a cook and a houseboy. And that’s what they called him, even when he was sixty years old. They called him a houseboy. They wouldn’t call him by his last name. Sound familiar?

In time, those common threads came to imbue Obama’s Presidential campaign with a kind of historical momentum, remaking it as something more vast than one man’s political ambitions: an index of progress itself. Yet that alignment, like the movement, came with other complications. Any true history of the movement that Obama spoke of must reckon with the government’s surveillance of its leadership—the sustained contempt and suspicion from J. Edgar Hoover and the bureaucratic overreach of his counterintelligence efforts to stall its momentum. Hoover’s F.B.I. saw an easy syllogism in which support for civil rights was evidence of Communist sympathies. The external threats of the Cold War lent authority to the paranoid suspicion that equality was a code word for Communism. The N.A.A.C.P. executive secretary Roy Wilkins, a political moderate and an outspoken anti-Communist, who addressed the march, had an F.B.I. file that dated back to the beginning of the Second World War. Bayard Rustin, who largely oversaw the logistics of the march, became a target of the bureau’s attention because of his youthful affiliation with the Communist Party, a connection that had been dormant long before that day on the Mall. Ralph Abernathy, the lieutenant to Martin Luther King, Jr., who’d helped to organize the Montgomery bus boycott, in 1955-56, had been watched since that action first attracted public attention. The surveillance files that the F.B.I. kept on King himself are extensive, and they betray an entrenched hostility toward both the man and the aspirations he represented. It went past mere surveillance—the F.B.I. planted bugs in King’s hotel rooms, then sent audio recordings of his extramarital trysts to his wife, Coretta, in an attempt to derail his efforts.

The Presidency of Barack Obama is the product of besieged citizens whose mail was read, whose telegrams were intercepted, whose phone calls were recorded and used against them. That irony doesn’t invalidate his legacy, but it does complicate the question of what was achieved on that August day five decades ago. If for no reason other than this, Obama’s position atop a dawning surveillance state should give him pause. That figures whose dissent consisted of a demand that the United States abide by its own Constitution could be vacuumed into a system meant to trace foreign threats raises the question of what other democratic demand, what present moral inconvenience, is being similarly thwarted. Barack Obama is, as he pointed out in Selma, an heir to the civil-rights movement. What he decides to do with that legacy is another matter.

Photograph: AP.