Peniel Joseph is the Barbara Jordan Chair in Ethics and Political Values and the founding director of the Center for the Study of Race and Democracy at the LBJ School of Public Affairs at the University of Texas at Austin, where he is also a professor of history. He is the author of several books, most recently "Stokely: A Life." The views expressed here are his. View more opinion articles on CNN.

(CNN) President John F. Kennedy's assassination 55 years ago this week permanently transformed American politics, thrusting the nation toward a long overdue -- and still unfinished -- reckoning with our democracy's painful history of violence and racism. For a brief moment, Kennedy's death produced a kind of national unity not seen since World War II, opening up political space for the new president, Lyndon Johnson, to push through watershed civil rights and voting rights legislation in 1964 and 1965.

Peniel Joseph

President Kennedy's death on November 22, 1963 in Dallas shocked many Americans out of the political stupor of the Eisenhower years, a time mythologized by some even today as as a sepia-toned era of economic plenty and cultural innocence. Kennedy's greatest legacy and contemporary tribute remains the fact that, during his final months as president, he embraced a liberated American future, one that is still being debated today but came one step closer to realization through the strength of his leadership.

The advent of the 1960s came at a moment when Cold War liberalism had identified the Soviet Union as America's greatest existential threat. President Kennedy's only inauguration speech bore out this logic; he famously observed that America stood prepared to "pay any price, bear any burden, meet any hardship, support any friend, oppose any foe to assure the survival and the success of liberty."

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But Kennedy's 1961 inaugural address focused on external threats just as domestic unrest stirred around racial justice and the struggle for black dignity. A televised address, almost 2½ years into his tenure, would be his finest moment as president. On June 11, 1963, against the backdrop of Alabama Gov. George Wallace's infamous threat to stand by the schoolhouse door to prevent the University of Alabama from being racially integrated, John Kennedy firmly and eloquently supported black citizenship.

Civil rights demonstrations and protests in Birmingham, Alabama, and cities across the nation inspired Kennedy to deliver the speech. The President, previously best known for his cool demeanor and piercing intellect, gave a rousing defense of racial justice that evening that characterized, following the words of the Rev. Martin Luther King Jr., the civil rights movement as a moral imperative. "A great change is at hand, and our task, our obligation, is to make that revolution, that change, peaceful and constructive for all," Kennedy said . "Those who do nothing are inviting shame as well as violence," he warned. "Those who act boldly are recognizing right as well as reality."

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