Martin Luther King Jr’s assassination on April 4, 1968 left behind a vacuum on the American left that has never been filled. The moral clarity he brought to debates about war, poverty, and rampant racism in American society has been subsumed for the last fifty years by a revanchist right wing and a timid liberalism that proposes small solutions to big problems.

The triple evils that King warned against — militarism, severe economic inequality, and white supremacy — have, in some ways, become more entrenched in the five decades since his death. No American political leader can say, on April 4, 2018, that the nation has adequately addressed the issues to which King dedicated most of his adult life. Meanwhile, the Left itself struggles to advance the arguments King articulated, or to update them for the twenty-first century. Yet King still matters for leftists — because his causes have been our causes for so long.

The push to create a King holiday in the late 1970s and early 1980s was important for two reasons. First, it forced Americans to acknowledge the role that King and the Civil Rights Movement played in shaping modern American society for the better. After 1968, the rise of Richard Nixon’s Southern strategy and the New Right — both of which propelled Ronald Reagan to the White House in 1980 — threatened to derail the precious progress made by African Americans. Activists and progressive politicians alike argued that a day of commemoration would make Americans think both about the progress that had been made and how much more needed to be done.

The holiday campaign was noteworthy for another reason. By the time the King holiday became federal law in 1983, the Left had suffered numerous defeats. Jimmy Carter’s presidency introduced doses of deregulation while failing to construct a coherent left coalition for the future. Reagan’s presidency had already built on the escalating tensions between the United States and the Soviet Union that defined the end of Carter’s term, while further starving Great Society–­era programs of desperately needed funding. A win, even for a symbolic holiday, was significant.

That same year, King’s legacy provided a source of inspiration for another event. The 1983 March on Washington, ostensibly a twentieth-anniversary celebration of the famed 1963 demonstration, doubled as a clarion call to the Left to organize themselves in Reagan’s America. Jesse Jackson’s speech was particularly powerful. Everyone knew he was a likely candidate for president in 1984. Yet he understood that the march was not simply an opportunity to garner support, but to articulate a new vision for the Left in the 1980s. “We must now dream a new dream,” he declared. “It must be an expanded dream.” His ambitious Rainbow Coalition — which proposed uniting civil rights and labor groups with other progressive movements — was the result. While too dependent on Jackson’s charismatic leadership, the movement was nevertheless a bright spot during a decade of conservative triumphs.

Since then the triple evils King warned of have only gotten worse. Militarism has triggered multiple wars in the Middle East and Central Asia with no end in sight. Economic inequality has spiraled out of control, with blacks in particular losing what gains they’d made. Racism has manifested itself in continued police brutality and brutally unjust institutions. It is this toxic brew King tried to stop. He died attempting to do so. It is up to the Left to use his legacy for something good today.

If the Left more generally has struggled to fulfill King’s legacy, so too has the African-American left in particular. The fall of the Black Power movement in the 1970s was followed by another abortive effort two decades later, in the late 1990s, in the form of the Black Radical Congress. An evolution of much of what King believed, the Black Radical Congress spoke against his triple evils while using the language of intersectionality and updating their analysis of American empire for the post–Cold War world. By the Iraq War, however, the organization had also fallen into disrepair, a victim of “war on terror” hysteria against dissent at home.

Other movements have suffered similar fates. Occupy Wall Street — born out of America’s inability to grapple with the inequality King warned about — faltered and then was crushed in 2011. The Black Lives Matter movement, always pushing against public opinion (much like the Civil Rights and Black Power movements), now must contend with the FBI’s labeling them as “Black Identity Extremists” — an eerie phrase that could’ve been taken out of J. Edgar Hoover’s playbook.

Even in the places where King fought his final battles, we see that the struggle against the triple evils has been a losing one. Back in the late 1960s, during his Poor People’s Campaign, King recruited members from Appalachia to represent the poorest of poor white Americans. They still suffer from extreme poverty today (while being denigrated as part of “Trump country,” despite considerable evidence to the contrary). King’s campaign in Chicago in 1966 against poor housing and dilapidated schooling for African Americans ended with a mixed victory. Today, America’s education and economic systems are as racially segregated as ever. Memphis, where King was working alongside striking garbage workers, is as racially divided in 2018 as it was in 1968. Atlanta, King’s home base of operations and the “City Too Busy to Hate,” remains fractured along class and racial lines.

King would undoubtedly be disappointed in how little so many of the problems he campaigned against have been dealt with today. But he was also aware that the movement to save America from its worse impulses would be a long, multigenerational one. And that it must include grappling with friends as well as enemies.

King’s careful and loving critique of Black Power is a good example. Before his assassination, King had given sermons and speeches, and written extensively about the roots of Black Power and where it, as a movement, could go as part of the broader black freedom struggle. While King, like many other civil rights leaders, criticized the movement in the summer of 1966, he soon turned from critique to understanding. King, informed by his visits to Watts in the aftermath of its riot in 1965 and his mixed success in the Chicago campaign of 1966, understood that the youth of black America were tired of Cold War liberalism’s broken promises.

The chapter “Black Power,” in his final book, Where Do We Go From Here, shows King trying to sketch out an alliance between Black Power advocates and older civil rights activists. King argued that Black Power was a “nihilistic philosophy born out of the conviction that the Negro can’t win.” He compared it to the Garvey movement of the 1920s, arguing that both “represent(ed) a dashing of hope . . . and a belief in the infinitude of the ghetto.” He feared that the call for separatism he saw in Black Power would preclude the possibility of building the interracial coalitions necessary for radical change. Still, King understood where the younger African-American activists were coming from. After all, some of them — including perhaps most notably Stokely Carmichael — began their activist careers as part of the Civil Rights Movement in the South. And he saw the need for Black Power in places such as Lowndes County, Alabama, as a way to bring about genuine change on a local level.

As the Left today wrestles with the relationship between a class-based politics and so-called “identity politics,” we would do well to remember that King saw the value in combining the two. Any nuanced, left critique of American society has to take into consideration the racial, class, and gender dynamics of America. The best of the Left’s activists and intellectuals have realized this (even though, at times, King himself fell short of this when it came to gender). While in many circles this is called intersectionality, it should in reality be called, quite simply, common political sense.

King’s debates with black nationalists, Black Power advocates, and others seeking radical change only sharpened his critiques of American society. In an era ripe for ideological change, we need the same type of careful, but forceful, criticisms of movements within the contemporary left — the kind of give-and-take that can bring to the surface the mélange of ideas necessary to take left-wing ideas mainstream.

New movements have tried to pick up the legacy left behind by King and others. William Barber’s attempt at a rebooted Poor People’s Campaign provides some hope that politicians will finally pay attention to the poverty too many Americans continue to face. The Medicare-for-All movement is fighting for a cause — quality, universal health care — that King staunchly supported. And with all the technological wonders of today, King’s words from his essay, “The World House,” provide something of a North Star for the Left’s priorities: “When scientific power outruns moral power, we end up with guided missiles and misguided men.”

Martin Luther King Jr spoke to many issues that still plague American society. The Left struggles to speak with the moral clarity and force that King once had — but that should not stop us from trying.