King's daughter on Monday encouraged Americans to fight for the slain civil rights leader's vision of love and justice "no matter who is in the White House."
In Atlanta, Bernice King addressed more than 2,000 people gathered at her father's Ebenezer Baptist Church four days before Donald Trump's presidential inauguration. She spoke on the same day that her brother, Martin Luther King III, met privately with the president-elect at Trump Tower in New York.
Trump won fewer than 1 out of 10 black voters in November after a campaign of racially charged rhetoric, and tensions have flared anew with his recent criticism of civil rights icon John Lewis, whom the president-elect called "all talk" and "no action."
Bernice King avoided a detailed critique of Trump, but said the nation still has a choice between "chaos and community," as her father once said.
"At the end of the day, the Donald Trumps come and go," Bernice King said. But, she added "we still have to find a way to create" what her father called "the beloved community."
The current Ebenezer pastor, the Rev. Raphael Warnock, avoiding calling Trump by name, but praised his predecessor. "Thank you, Barack Obama," he said. "I'm sad to see you go."
In South Carolina, speakers at a state Capitol rally reminded attendees that minority voters' power at the ballot box has never been more important, while some attendees expressed unease about Trump joining the Republican majorities that control Capitol Hill.
"It's going to be different, that's for sure," said Diamond Moore, a Benedict College senior who came to the Capitol. "I'm going to give Trump a chance. But I'm also ready to march."
Martin Luther King III told reporters in New York that his meeting with Trump was "productive." He said Trump pledged to be a president for all Americans, but King III added "we also have to consistently engage with pressure, public pressure" because "it doesn't happen automatically."
Back in Atlanta, Sen. Bernie Sanders brought the Ebenezer assembly to its feet with his reminder that King was not just an advocate for racial equality, but a radical proponent for economic justice - a mission that put him at odds with the political establishment.
"If you think governors and senators and mayors were standing up and saying what a great man Dr. King was, read history, because you are sorely mistaken," roared Sanders, who invoked the same themes from his failed presidential campaign.
Sanders, who struggled to attract black voters in his Democratic primary fight with Hillary Clinton, recalled King opposing the Vietnam War as exploiting the poor. He also noted King was assassinated in Memphis, Tennessee, where he'd gone to rally striking sanitation workers, white and black.
Truly honoring King, Sanders said, means bringing that "spirit and courage into the arena in 2017."
Activist priest Michael Pfleger, himself a self-described radical, built on Sanders' message with a 45-minute keynote message indicting the nation's social and economic order - a structure he said would get worse under Trump.
The Chicago priest said "white hoods" of the Ku Klux Klan "have been replaced by three-piece suits." He bemoaned high incarceration rates, a "militarized, stop-and-frisk police state," profligate spending on war, and a substandard education system.
Pfleger said many Americans too quickly dismiss violence in cities as the fault of those who live there, when the real culprit is poverty. "If you put two lions in a cage and you don't feed them," he said, "one will kill the other in the pursuit of survival."
Warnock, meanwhile, zeroed in on Trump for his treatment of Lewis, now a Georgia congressman who represents most of Atlanta.
Lewis angered Trump when he told NBC's "Meet the Press" that he views Trump as "illegitimate" because of alleged Russian interference in the campaign. Trump retorted on Twitter that Lewis is "all talk" and said his district is "falling apart" and "crime infested."
"Anybody who suggests that John Lewis is all talk and no action needs a lesson in American history," Warnock said, notably declining to say the president-elect's name.
As a young man, Lewis was arrested and beaten by authorities as he demonstrated for civil and voting rights for black Americans.
Lewis was in Miami at King Day events.
Some Republicans have defended Trump's criticism of Lewis, arguing it is inappropriate for a congressman to question an incoming president's legitimacy.
Clara Smith, an Atlanta resident who came Monday to Ebenezer, scoffed at any GOP indignation, remembering that Trump for years questioned whether Obama was a "natural born citizen" as the Constitution requires.
"He carried on with that knowing full well what he was doing" to the first black president, Smith said.
Smith, 66, recalled joining sit-ins and lunch counters of segregated restaurants in her hometown of Louisville, Kentucky. She said she tries to "ignore" Trump and "his foolishness with the Twitter," but "with everything that's happening around us ... we have to pass along that history."
Elsewhere, residents in Memphis are honoring King with neighborhood clean-up events and a daylong celebration at the National Civil Rights Museum.
Bicyclists in Detroit have marked the day by pedaling to sites connected to a historic visit King made to the city.
Meantime in New York City, volunteers through Habitat for Humanity used the day to do some good for others.