COLUMBIA, S.C. — Eight of the Democratic presidential candidates locked arms in a brief demonstration of unity Monday amid some of the most intense intraparty sparring to date as they marched in honor of Martin Luther King Jr.

A week after Sens. Elizabeth Warren, D-Mass., and Bernie Sanders, I-Vt., questioned each others' honesty on a debate stage, the two shared a warm greeting outside Brookland Baptist Church before marching toward the state Capitol building for the annual civil rights rally held on the federal holiday commemorating King.

Former Vice President Joe Biden also offered a handshake and a smile to Sanders, two days after he called on Sanders' campaign to retract what he called a "distorted" video clip questioning his commitment to protect Social Security.

It could have some of the candidates' last trips to South Carolina as presidential contenders, as Iowa's first-in-the-nation caucuses on Feb. 3 loom as a critical test for those lagging in polling, fundraising or both. The senators who were on hand — Sanders, Warren and Amy Klobuchar, D-Minn. — also have to contend with the time crunch imposed by their obligations to sit as jurors for most of the next few weeks in President Donald Trump's impeachment trial.

"I know as I get on that plane back to Washington, D.C., and sit in that chamber that I will not stand alone," Klobuchar told the crowd. "We go on behalf of the people of this great nation. We go on behalf of the truth. We go on behalf of justice."

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Polls in South Carolina, which hosts the "first in the South" primary on Feb. 29, show Biden with a commanding advantage thanks to his strong and resilient support among African American voters. In his remarks, he recalled the sometimes violent struggle for civil rights decades ago as he warned about what is at stake if Trump is allowed four more years in the White House.

"It's not snarling dogs that brought us to the inflection point. It's Donald Trump's poisonous, divisionist politics," Biden said. "We have a tremendous opportunity to take the next great step forward in racial justice, criminal justice, domestic justice, environmental justice."

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Sanders, whose support has grown among younger African American voters, told the crowd that King's work was as much about economic justice as it was racial justice, calling King a "nonviolent revolutionary."

"He took on the entire political establishment. He took on the economic establishment. And he fought racism every step of the way," Sanders said. "Our job is not just to remember the history of Dr. King. It is to absorb his revolutionary spirit and apply it today. And that means we will fight racism in every part of American society."

The billionaire businessman Tom Steyer, who has surged in recent South Carolina polls, urged his rivals to cease their attacks on one another.

"This is not the time for the people who are running for president to bicker with the other or complain. It's not time for wine caves and old stories and old videos," he said. "This is a time where we have a job: beat Mr. Trump. There's no question about that."

Warren focused on "this dark moment of Donald Trump," saying America was ready to move beyond it.

"America is ready not to go back to an old system of racism and economic injustice that was broken long before Donald Trump showed up. America is ready to go forward, to write the next chapter of our history," she said.

Pete Buttigieg, the former mayor of South Bend, Indiana, attended several church services in Columbia on Monday and joined his rivals in marching on the Capitol, but he did not speak as he hustled back to Iowa to attend another MLK Day event in Des Moines. Most of the other candidates were expected to follow him.

The march in Columbia started two decades ago as a counterdemonstration against a rally planned to support the Confederate battle flag that had flown over the Capitol.