In a moving farewell speech before an enormous crowd in Chicago last week, President Obama evoked the American creed of unity and aspiration as the foundation of our democracy. He has always embraced a vision of America as a “melting pot.”

Mr. Obama embodied for many Americans the legacy of the Rev. Dr. Martin Luther King Jr., whom we celebrate on Monday. Our national memory of Dr. King has, for nearly 50 years, reinforced the belief that America, unlike any other nation, could extend opportunity to everyone regardless of his or her identity. In Dr. King’s name, assimilation and aspiration have been the keywords of the post-civil rights era, and diversity and inclusion its currency. And Mr. Obama has symbolized more than anyone in American history the idea that racial representation and the content of one’s character were the perfect antidote to racism.

It’s true that, in fulfilling the duties of the presidency with great dignity, Mr. Obama represents the highest expression of the goal of assimilation. But for African-Americans, he was also the ultimate lesson in how this antidote alone is insufficient to heal the gaping wounds of racial injustice in America. It’s clear that black leadership, in itself, isn’t enough to transform the country. So we must confront the end of an era and the dawn of a new one.

We now live in a post-assimilation America. The 50-year-old rules for racial advancement are obsolete. There is no racial barrier left to break. There is no office in the land to which an African-American can ascend — from mayor to attorney general and the presidency — that will serve as a magical platform for saving black people and our nation’s soul from its racist past. We cannot engineer a more equitable nation simply by dressing up institutions in more shades of brown. Instead, we must confront structural racism and the values of our institutions.

Mr. Obama’s election was by any historical measure the apex of the civil rights period — so many black, white, Latino and Asian-Americans saw him as the fulfillment of Dr. King’s vision. The notion that the blood and courage of civil rights heroes had led to that moment was captured by the iconography of the campaign. Obama supporters from Atlanta to Chicago wore T-shirts illustrated with the profiles of Dr. King and Mr. Obama side by side. Jay-Z expressed the liturgy of the age in verse: “Rosa Parks sat so Martin Luther could walk/Martin Luther walked so Barack Obama could run/Barack Obama ran so all the children could fly.”

But the exceptionalism of Mr. Obama’s biography couldn’t save us from the Tea Party revolution, Republican obstructionism, police brutality, voter suppression and Islamophobia. We now know that no individual, no matter how singular, can bend the moral arc of the universe. Not even Dr. King could.

The Dr. King we choose to remember was indeed the symbolic beacon of the civil rights movement. But the Dr. King we forget worked within institutions to transform broken systems. He never positioned himself as a paragon of progress. Nor did he allow others to become complacent.

In his last book, in 1967, “Where Do We Go From Here: Chaos or Community?” Dr. King warned that the movement was already hobbled by delusion. “The majority of white Americans consider themselves sincerely committed to justice for the Negro,” he wrote. “They believe that American society is essentially hospitable to fair play and to steady growth toward a middle-class utopia embodying racial harmony. But unfortunately this is a fantasy of self-deception and comfortable vanity.”

Dr. King never imagined the election of African-Americans to office in itself as sufficient. Instead, his “unarmed truth” was the need to remake all of American society. He urged us to become “creative dissenters” and hold the country “to a higher destiny.”

So what does creative dissent look like in a post-assimilation America?

We must recognize that institutions are far more powerful than individuals, no matter how many people of color can be counted in leadership. Structural racism is immune to identity politics. That Eric Holder and Loretta Lynch became attorneys general, for example, was the starting point for the possibility of federal criminal justice reform — not the reform itself.

In addition, history matters. Black people in charge of, or embedded in, institutions that have not atoned for their history of racism can make it easier for those institutions to ignore or dismiss present-day claims of racial bias. That’s because the path to leadership has often meant accepting institutions as they are, not disrupting them. Consider what black Harvard Business School alumni told the journalist Ellis Cose: A key to success is “never talk about race (or gender) if you can avoid it, other than to declare that race (or gender) does not matter.”

As the failure of the black political leadership in Baltimore to protect black lives and the limited ability of black police chiefs to curb brutality in their own departments demonstrate, people of color can inherit or perpetuate structures of inequality. Many institutions of government, finance and higher education were built on the backs of enslaved African-Americans and remain haunted by that history. Diversity and inclusion policies, therefore, should grow out of truth and reconciliation practices as well as strategic hiring plans. Intentional transformation, even reparations, one government agency, one company, one college at a time moves us past the denial and the empty promises and will take us closer to where Dr. King wanted America to go.

Georgetown University’s decision to make reparations for its past is a powerful expression of creative dissent. Last year, after its president met with descendants of the enslaved African-Americans owned by the university he declared, “We cannot do our best work if we refuse to take ownership of such a critical part of our history.” Georgetown will provide preferential admissions to descendants, akin to legacy status for the children of alumni.

Other colleges should take heed. The measure of institutional change will not simply be a new diversity task force or more faculty members of color. We should judge transformation by how our institutions behave on behalf of individuals rather than the other way around.

Some Black Lives Matter activists have already embraced the possibilities of the new era. “We don’t need more elected officials that are just black,” Charlene Carruthers, national director of the Black Youth Project 100 in Chicago, said to a reporter. “We need champions in the city.”

Mr. Obama himself seems ready to move on from the era of assimilation. In his farewell speech, there was no more self-congratulatory praise for a country that gave him a chance to be president. Instead, he acknowledged, for the first time, the very real threat of racism to our democracy and the contingent nature of racial progress.

In a revision to the American creed, he added, equality may be self-evident but it has “never been self-executing.” And he listed specific areas where systemic racism needed to be uprooted, which he hadn’t done in his State of the Union addresses or inaugural speeches: “If we’re going to be serious about race going forward, we need to uphold laws against discrimination — in hiring, and in housing, and in education and in the criminal justice system.” As it turns out, there is no straight line of progress from Seneca Falls to Selma to Stonewall.

In post-assimilation America, people of color must continue to pursue leadership roles as the demographics of the nation inexorably change. But they must also reject their personal achievement as the core measure of progress and instead use history as a tool to measure systemic change. To proceed otherwise is to perpetuate the “fantasy of self-deception” that Dr. King rejected.

The future is no longer about “firsts.” It is instead about the content of the character of the institutions our new leaders will help us rebuild.

Khalil Gibran Muhammad is professor of history, race and public policy at the Harvard Kennedy School and the author of “The Condemnation of Blackness: Race, Crime and the Making of Modern Urban America.”