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.