Fifty-one years ago, when Dr. Martin Luther King Jr. became a martyr in the struggle for beloved community and multiethnic democracy, few imagined that he would, within a half century, achieve the status of a founding father on the National Mall. Dr. King had long been a target of J. Edgar Hoover’s FBI and was no longer on speaking terms with President Lyndon Johnson. He had been put out of his own church denomination and was rejected by many civil-rights organizations because he questioned the violence of the war economy in Vietnam. We cannot celebrate him today alongside Lincoln and Jefferson without recognizing how he showed us that America’s experiment in democracy has always required radical struggle to move us toward a more perfect union. Indeed, to honor King’s legacy today is to reread our tradition in the light of his radical witness.

King is most famous for the sermonic flourish of “I have a dream,” which he added at the last minute to his address at the 1963 March on Washington. But the central argument of his remarks that day was that the United States had not lived up to the ideals that we had written into our founding documents. King was not naive. His appeal to constitutional ideals did not depend on a false belief that the white men who signed their names to those documents had ever been faithful to them. But King understood that what any people puts down on paper can become a basis for public accountability.

A nation founded in revolution must always remain open to reassessment in order to remain true to itself. King and the fusion movement he led forced the institutions of white supremacy to remember, as the Declaration of Independence had said, that “whenever any Form of Government becomes destructive…it is the Right of the People to alter or to abolish it.” Any law or custom that does not recognize the equality of all people under the law must be altered, King argued. This wasn’t an attack on government but an insistence that it live up to its expressed commitment “to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity.” This wasn’t simply the hopes and dreams of the down-trodden. It was what America claimed to be for all people.

King’s understanding of American history saw clearly that the nation established in revolution had only survived and improved itself through Reconstruction. Whatever his intentions, Abraham Lincoln’s great achievement in the Civil War wasn’t simply the preservation of the Union but also the expansion of democracy to the formerly enslaved. His prayer for a “new birth of freedom” at Gettysburg had been answered in the 13th, 14th and 15th Amendments and in Reconstruction governments across the South that imagined access to education, health care, and living wages for poor black and white workers. The “Redemption” movement that overthrew Reconstruction was, on this read, deeply anti-American, just as the resistance to civil rights that King had faced throughout the South was contrary to the fundamental promises of democracy.

This is why King’s colleague in the movement, Fannie Lou Hamer, could speak to the nation with moral authority when she asked at the 1964 Democratic National Convention, “Is this America, the land of the free and the home of the brave, where we have to sleep with our telephones off the hooks because our lives be threatened daily, because we want to live as decent human beings?” The coalition of poor black and white people that had come to be seated had more constitutional right to represent Mississippi than its official all-white delegation, Hamer insisted. She was insisting that America needed a moral revolution of values in order to become what we claim to be.

What King and Hamer named half a century ago, we must find a way to make clear today. The moral and constitutional crisis we face in America is not just about Republicans versus Democrats or liberal versus conservative. It is, instead, about right versus wrong. We are in a struggle for the heart and soul of this nation. And, in a real sense, we face the question of whether America can be.

For half a century, political operatives who paved the way for Trumpism have used Richard Nixon’s Southern strategy to pit black, brown, and white people against one another. They have hijacked our moral narrative to frame narrow cultural differences as the only moral issues in public life. And they have tried to paint the resistance to their consolidation of power as “anti-American.”

We who are the heirs of King and Hamer know that we cannot remain silent while America’s experiment in democracy is trampled by those who pretend to honor its founders.

The direction of the nation must be altered when 140 million live in poverty and low wealth. When systemic racist voter suppression and gerrymandering work in collusion to keep extremists in office despite new demographic progressive majorities. We must expand health care to all, provide just immigration policies, and curb gross militarism. This is why we have relaunched the Poor People’s Campaign of 1968 to honor the work King was doing at the end of his life by insisting that it is still needed today. Our work today echoes the call for radical commitment that Dr. King noted in his last sermon, the day before his death, when he said that in the fight for true democracy, “nothing would be more tragic than for us to turn back now.”

Black, white, and brown, gay, trans, and straight, as people of faith and people who believe in the moral arc of the universe, we are standing together to say that America’s future depends on yet another revolution—a movement of people committed to reconstructing democracy and guaranteeing equal protection under the law for all people. This is what those who struggled before us fought and died for. We must not be satisfied with anything less. It’s our time now.