Against the advice of some of his closest advisers, King had condemned the Vietnam War, and in the process alienated President Johnson, who'd done more for African Americans than any president since Lincoln.
Also against the wishes of many supporters, King was planning a "Poor People's March on Washington." By that March, King's dream had left him sleepless, lonely, depressed and discouraged, according to several biographers, including David Garrow, author of Bearing the Cross.
Many critics felt that his movement was out of focus and out of steam, and that his notion of non-violent change had been discredited by urban riots and black militancy, Garrow said. "It was a terrible time for him. He was phenomenally exhausted. He'd carried on a presidential campaign pace for 15 years."
King also was pessimistic about the direction of the nation and haunted by fear of failure, Garrow said. When he was assassinated April 4 in Memphis, some viewed it less as a premature end than a merciful release.
"I was almost strangely relieved when Martin died," his aide, Andrew Young, said later. "This was the only way he could know peace." King counselor Chauncey Eskridge told Garrow that "Andy and I said that maybe this was the best thing, because he'd run out of things to do."
Four decades later, here's what happened Sunday in the four churches where King preached:
Atlanta: Ebenezer Baptist
Raphael Warnock grew up hearing about King, studying him, trying to emulate him.
On Sunday, speaking as King's successor as senior pastor at "America's Freedom Church," he drew a historical line from the biblical figure of Joseph to King to Obama — all dreamers, he said, who saw something better for their people.
Warnock called his sermon Dreams from our Fathers, a variation on Obama's memoir, Dreams from My Father.
Warnock told a racially diverse congregation that Obama "would not be possible were it not for one who dared to challenge the conscience of a nation with four simple words: 'I have a dream.' "
With the congregation's fervor rising on each name, Warnock listed others on whose shoulders Obama stands, from "Jewish immigrants who came through the Holocaust and said, 'Never again,' " to slain civil rights leader Medgar Evers, "who died in his driveway fighting for freedom."
He added a caution: "Joseph was a dreamer. And so his brothers tried to kill him. And don't you know that that's what we do to dreamers. We try to destroy dreamers, lest dreamers destroy the status quo. We love dreamers after they are dead. But while they are alive we try to destroy them."
And yet: "Come Tuesday, we will have sitting in the Oval Office a dreamer-in-chief," he said. "It's been a looong time coming, but I know — not because Sam Cooke said it, but because God said it — I know a change is gonna come."
The congregation closed by singing We Shall Overcome.
"Most people probably weren't like Martin Luther King Jr. during his time. They didn't believe his dream could come true," said Jonathan Boykin, whose family drove from Tennessee for the service. His sister Kandi said King "would be proud of the progress we've made. At the same time, he would remind us that there's still a lot of work to be done."
Los Angeles: Holman United Methodist
"Who is Number 44?" pastor Leonardo Wilborn asked at the start of the service.
"Barack Obama!" the congregation shouted in unison.
"Amen," the preacher replied.