Former secretary of state Hillary Clinton, center, the Rev. Jesse Jackson and Rep. Sheila Jackson Lee (D-Tex.) march over the Edmund Pettus Bridge in Selma, Ala., on Sunday. (Melina Mara/The Washington Post)

SELMA, Ala. — Several Democratic presidential hopefuls came here to a resonant remembrance of one of the bloodiest moments of the civil rights movement on Sunday, with Sen. Cory Booker talking emotionally about being a descendant of slaves and others urging a renewed defense of voting rights.

The event was an opportunity for 2020 candidates to reach out to African American voters. But for some of the day, the focus was not on the party’s future but on its past nominee, Hillary Clinton, and a display of the lingering tension between her and her 2016 primary rival, Sen. Bernie Sanders.

Booker, one of two African American candidates in the presidential race, tied his identity to the country’s record of slavery and racism in an appearance that connected a difficult history with the current political moment.

“My roots go back to slavery,” he said. “Rose up from poverty and segregation, hardship and pain. Rose up in black churches, in civil rights organizations.”

Booker hinted at the words of Martin Luther King Jr. to draw attention to what he depicted as a resurgence of racial animosity.

“The dream is under attack. The dreamers are in danger,” Booker said. “And we need each other more than we realize in this country.”

Selma has become an annual pilgrimage site for Democratic politicians, culminating with a walk across the Edmund Pettus Bridge, where on March 7, 1965, marchers advocating for voting rights were attacked by police in a day that has become known as Bloody Sunday. The Voting Rights Act was signed the same year. This year, the events marking one of the most searing moments of the civil rights movement took place over four days, including a Jubilee Golf Tournament on Friday and a “battle of the bands” on Saturday.

The main event, Sunday’s march across the bridge with linked arms, call-and-response, and gospel songs, was nearly derailed by thunderstorms. But the weather cleared enough for thousands to make the walk.

A trio of potential presidential candidates — Sanders of Vermont and Booker of New Jersey, who have announced their campaigns, and Sen. Sherrod Brown of Ohio, who is considering a bid — were here along with Clinton during the day’s events.

Booker told his personal story in the context of the broader civil rights movement, recounting how his parents faced discrimination in the 1960s as they attempted to buy a home in a white neighborhood in New Jersey. A white lawyer who helped his family at the time, he said, was inspired by the events in Selma.

“People feel the forces tearing us apart are greater than those bringing us together,” Booker said. “It’s time for us to defend the dream. It’s time that we dare to dream again in America.”

Clinton appeared at a “unity breakfast” in her honor. While some strategists believe her 2016 campaign struggled in part because of a failure to turn out enough African American voters, no such lack of enthusiasm was on display Sunday.

A small choir serenaded Clinton with a song about moving forward, rising up, and climbing higher mountains. “Hillary,” one verse went, “you’re still rising.” One speaker made a request for “when” she is president. Another outlined a justification for inducting her into the National Voting Rights Museum Women’s Hall of Fame. Some wore T-shirts that said, “Hillary is my president.”

“She was elected president of the United States, and it was stolen from her,” said state Sen. Hank Sanders, as a breakfast crowd of about 700 rose to its feet. “It was stolen from her by the FBI. . . . It was stolen from her by the Russians.”

The interaction between Sanders and Clinton — their first since they faced off in a sometimes-bitter 2016 Democratic primary — was frosty. While Clinton gave Booker an effusive hug, the exchange with Sanders was brief; as he passed by quickly, she reached out and initiated a terse hello.

The lingering tension between Sanders and Clinton has reemerged in recent days. Sanders was asked on Friday whether he plans to meet with Clinton, as others seeking the Democratic nomination have done.

“I suspect not. Hillary has not called me. Look, we have differences,” Sanders said on ABC’s “The View.” Asked if he was interested in her advice, he responded, “I think not.”

“Hillary and I have fundamental — you know, fundamental differences,” he said. “And that’s what it is.”

Sunday’s events provided a forum for the belief among many African American leaders that the GOP has been launching a renewed fight against voting rights, with such measures as voter ID laws and the curtailment of early voting.

“Make no mistake: We are living through a full-fledged crisis in our democracy,” Clinton said. “There may not be, thank God, tanks in the streets. But what’s happening goes to the heart of who we are as a nation.”

She also said more work needs to be done “when racist and white supremacist views are lifted up in the media and in the White House, when hard-fought-for civil rights are being stripped back.”

Clinton said voter suppression had an impact on her fortunes in 2016.

“We know candidates, both black and white, have lost their races because they have been deprived of the votes they otherwise would have gotten,” she said.

The morning unity event — called the Martin and Coretta King Unity Breakfast — was held at a community college named after George Wallace, the segregationist Democratic governor who four times ran unsuccessfully for president.

“How sad it is that 54 years later, we are still fighting for the right to vote,” Sanders said. “It’s our turn to demand that we end all voter suppression in this country.”

During the breakfast, Sanders mostly sat at a table watching the speakers as Booker made the rounds, mingling at various tables, hopping onto the stage to exchange whispers with the Rev. Jesse Jackson, and posing for selfies with anyone who asked.

Brown, who told reporters that he will decide on a presidential bid by the end of March, also circulated among the mostly African American attendees, asking about their lives.

Asked how he could compete in a diverse field of candidates, and with an increasingly diverse electorate, Brown said he would let his record speak for itself.

“If I run, I’ll be the only Democrat on that stage who voted against the Iraq War. I’ll be the only Democrat on that stage who supported marriage equality 20 years ago. I’ll be the only person on that stage who has a longtime F from the NRA,” Brown said. He pointed to his face. “I can change a lot of things, but I can’t change this part of me, right?”

David Weigel contributed to this report.