"His good name will be honored for as long as the creed of America is honored. His message will be heard and understood for as long as the message of the gospels is heard and understood."
Like McCain, Democratic Sen. Hillary Rodham Clinton traveled to Memphis to observe the day. But unlike him, she chose not to speak at ceremonies at the Lorraine Motel where King was shot.
Instead, she was in the church where he had delivered his final sermon on the day before his death. A college student 40 years ago, Clinton recalled, "I walked into my dorm room and took my book bag and hurled it across the room." Her voice breaking, she added, "It felt like everything had been shattered and we'd never be able to put the pieces together again."
In a glancing reference to the current campaign, she added that "because of him, after 219 years and 43 presidents who have all been white men, this generation will grow up taking for granted that a woman or an African-American could be president of the United States."
Alone among the three, Sen. Barack Obama decided against a personal pilgrimage to the city of King's death. The strongest black candidate in history, he campaigned in Indiana, where he said King's pleas have yet to be answered fully.
"You know, Dr. King once said that the arc of the moral universe is long, but it bends toward justice. ... But here's the thing - it does not bend on its own. It bends because each of us in our own ways put our hand on that arc and we bend it in the direction of justice," said the Illinois senator.
"So on this day of all days let us each do our part to bend that arc. Let's bend it toward justice. Let's bend that arc toward opportunity. Let's bend that arc toward prosperity for all."
Race has been a constant, occasionally divisive companion to the Democratic campaign for the White House, and McCain's decision to speak at ceremonies held by the Southern Christian Leadership Conference was intended to demonstrate an eagerness to appeal to black voters who have long shunned Republicans.
For her part, Clinton has struggled to gain black votes in her competition with Obama. Additionally, some prominent black figures criticized her last winter for saying that it took a white man, President Lyndon B. Johnson, to finally win passage of the 1964 Civil Rights Act.
Obama's political imperative was different. He frequently recalls King's use of the phrase "the fierce urgency of now" as a motivation for his own candidacy for president. Yet particularly in the wake of controversy over his former pastor's rhetoric and his own major speech on race last month, he has sought to avoid narrowing his electoral appeal by being seen solely or even predominantly as a black candidate.
There was a scattering of boos as McCain spoke in front of the balcony where King was mortally wounded, but approving calls of "Amen" also floated up from a crowd huddled under umbrellas in a drenching rain.
"No good cause in this world - however right in principle or pure in heart - was ever advanced without sacrifice. And Dr. King knew this," McCain said.
"... He was a man accustomed to the nearness of danger. And when death came, it found him standing upright, in open air, unafraid."
McCain said King "was called an agitator, a troublemaker, a malcontent, and a disturber of the peace.
"These are often the terms applied to men and women of conscience who will not endure cruelty, nor abide injustice. We hear them to this day - in Darfur, Zimbabwe, Burma, Tibet, Iran and other lands - directed at every brave soul who dares to disturb the peace of tyrants."
And yet, he said, "We can be slow as well to give greatness its due, a mistake I made myself long ago when I voted against a federal holiday in memory of Dr. King. I was wrong and eventually realized that, in time to give full support for a state holiday in Arizona."
Clinton, who grew up the daughter of conservative Republicans, recalled once meeting King as a teenager.
"I stood in line for a very long time that night to shake his hand," she said. "He was gracious, he was kind to lean over to shake the hand of a 14-year-old girl from the suburbs of Chicago who went to an all-white church, an all-white school, and lived in an all-white suburb.
"But he didn't ask me as he reached out for my hand, 'Where do you live, what's your experience.' He just took it and looked in my face and thanked me for coming."
Obama, too, linked King's work to the present, saying the dream of economic justice is "still out of reach for too many Americans."
From his campaign platform in Fort Wayne, Ind., Obama also recalled the impact that Robert Kennedy, a white politician running for president, had on the night King was shot.
"It fell to him to inform a crowded park (in Indianapolis) that Dr. King had been killed," Obama said.
"And as the shock turned toward anger, Kennedy reminded them of Dr. King's compassion, and his love. And on a night when cities across the nation were alight with violence, all was quiet in Indianapolis."
In her remarks, Clinton pledged as president to appoint a high-level "poverty czar" - a job perhaps tailor-made for John Edwards, a former Democratic primary rival who stressed the eradication of poverty during his campaign. Both Obama and Clinton have sought Edwards's endorsement. "I believe we should appoint a cabinet level position that would be solely and fully devoted to ending poverty as we know it in America," Clinton said.
