The Rev. Dr. Martin Luther King Jr.’s “I Have a Dream” so disturbed the American power structure that the F.B.I. started spying on him in what The Washington Post called “one of its biggest surveillance operations in history.” The speech even moved the head of the agency’s domestic intelligence division to label King “the most dangerous Negro of the future in this nation from the standpoint of Communism, the Negro and national security.”Of course, King wasn’t dangerous to the country but to the status quo. King demanded that America answer for her sins, that she be rustled from her waywardness, that she be true to herself and to the promise of her founding.

King was dangerous because he wouldn’t quietly accept — or allow a weary people to any longer quietly accept — what had been. He insisted that we all imagine — dream of — what could and must be.

That is not the mission of politicians. That is the mission of a movement’s Moses.

And those Moses figures are often born among the young who refuse to accept the conditions of their elders, who see injustice through innocent eyes.

King was just 34 years old in 1963.

As President Obama put it Wednesday:“There’s a reason why so many who marched that day and in the days to come were young, for the young are unconstrained by habits of fear, unconstrained by the conventions of what is. They dared to dream different and to imagine something better. And I am convinced that same imagination, the same hunger of purpose serves in this generation.”So now, America yearns for more of these young leaders, and in some ways it has found some, not just in the traditional civil rights struggle but also in the struggles to win L.G.B.T. rights and to maintain women’s reproductive rights.

Yet there remains a sort of cultural complacency in America. After young people took to the streets as part of the Arab Spring, many Americans, like myself, were left wondering what had become of American activism. When was the last time our young people felt so moved that they took to the streets to bring attention to an issue?There were some glimmers of hope around Occupy Wall Street and the case of Trayvon Martin, but both movements have lost much of their steam, and neither produced a clear leader.

So as we rightfully commemorate the March on Washington and King’s speech, let us also pay particular attention to the content of that speech. King spoke of the “fierce urgency of now,” not the fierce urgency of nostalgia.

(I was struck by how old the speakers skewed this week during the commemorations.)What is our fierce urgency? What is the present pressure? Who will be our King? What will be our cause?There is a litany of issues that need our national attention and moral courage — mass incarceration, poverty, gun policy, voting rights, women’s access to health care, L.G.B.T. rights, educational equality, immigration reform.

And they’re all interrelated.

The same forces that fight to maintain or infringe on one area of equality generally have some kinship to the forces that fight another.

And yet, we speak in splinters. We don’t see the commonality of all these struggles and the common enemies to equality. And no leader has arisen to weave these threads together.

Martin Luther King was a preacher, not a politician. He applied pressure from outside the system, not from within it. And I’m convinced that both forms of pressure are necessary.

King’s staggering achievement is testament to what can be achieved by a man — or woman — possessed of clear conviction and rightly positioned on the side of justice and freedom. And it is a testament to the power of people united, physically gathering together so that they must be counted and considered, where they can no longer be ignored or written off.

There is a vacuum in the American body politic waiting to be filled by a young person of vision and courage, one not suckled to sleep by reality television and social media monotony.

The only question is who will that person be. Who will be this generation’s “most dangerous” American? The country is waiting.