Opinion polls suggest the competition for the crucial voting bloc will be far more intense than in 2008 and 2016

Dionne Whitby, a black teacher, was waiting in a school gym, an air conditioned refuge from the Florida heat, for a union meeting on the eve of the first Democratic presidential primary debate. She admires Senators Cory Booker and Kamala Harris, she said, but will probably vote for Joe Biden.

“I love both of them but I don’t think they’d be able to beat Trump because of popularity, race, gender – some of the reasons that Hillary didn’t win,” Whitby, 36, said in North Miami, a majority African American city. “I think Biden should take one of them as his vice-president.”

The comment illustrated the difficult calculus for a critical voting bloc when the most diverse field of presidential candidates in history takes the stage here on Wednesday and Thursday nights.

Opinion polls suggest the competition for African American voters will be far more intense than in 2008, when Barack Obama dominated against Hillary Clinton, or in 2016, when Clinton trounced Bernie Sanders.

Democrats look for that old debate magic – but can anyone defeat Trump? Read more

Biden, 76, who long championed civil rights and was himself vice-president under Obama, remains the current favourite among black voters, apparently drawing particular supporters from older voters who backed Bill and Hillary Clinton and Obama. He is seen by many as the pragmatic and safe choice in a year when nothing can be left to chance against Donald Trump, viewed by many as racist, xenophobic and winking at white supremacists.

But there is still plenty of time for others, including the two African American candidates, to make inroads. Booker, 50, from New Jersey, has made gun violence and criminal justice reform central pillars of his campaign. Harris, 54, from California, who gets the chance to go toe to toe with Biden on Thursday, emphasises a personal biography that includes parents active in the civil rights movement and student days at the historically black Howard University in Washington.

Clinton had a clear lead over Obama among black voters in late 2007 but, when he won the first caucuses, in Iowa, and made clear he had a genuine chance, the tide turned in his favour. Some believe the same could happen for Booker or Harris.

House of Representatives majority whip Jim Clyburn, whose annual fish fry in South Carolina drew 21 candidates last Friday night, told the Guardian: “In spite of what may be said to the contrary, Barack Obama won the South Carolina primary real big on the night he won the Iowa caucuses. He demonstrated in Iowa that he had viability and I think that the same could take place here. The performance levels that were reached by those two in Iowa will determine their fortunes in South Carolina.”

Harris supporter Paul Fletcher, a teacher who put a question to candidate Beto O’Rourke at Tuesday’s union meeting in North Miami, recalled that black leaders in the Democratic party had initially be sceptical of Obama.

“All the same people were telling young people it wasn’t Obama’s time and he had to wait. Hillary Clinton had all the super delegates and all the money but he had a new idea about how to raise money through the internet. A lot of black politicians had to come back and apologise. They miscalculated just like they continue to do.”

Facebook Twitter Pinterest Joe Biden speaks to the crowd in Columbia Photograph: Sean Rayford/Getty Images

He added: “Biden appeals to the Obama and Clinton constituencies. They aren’t the most progressive. They’re still trying to figure out how they lost the last one and, if they continue as they are, they might find a similar outcome.”

Fletcher, 72, from Hollywood in Florida, backed Sanders last time and described the political establishment as out of touch. “They used to talk about hip-hop music bringing down the community. Now they all want money from Jay-Z and Beyonce.”

Quick guide Who are the leading Democrats running for 2020? Show Hide Joe Biden, former vice president Biden unsuccessfully ran for the nomination in 1988 and 2008, and his campaign is likely to be dogged by controversy after allegations from several women they were left feeling uncomfortable by their physical interactions with him. If successful, Biden would become the oldest person to be elected president in US history. Mike Bloomberg, former New York mayor Bloomberg has expressed concern that none of the top candidates can defeat Trump, and he aims to make up for an unusually late entry in the Democratic primary with historic spending of hundreds of millions of dollars in television ad time and an unorthodox strategy of skipping the first four states in the primary. Bloomberg has announced that his campaign will be entirely self-funded, but can this billionaire win? Amy Klobuchar, Minnesota senator On Election Night 2018, Klobuchar coasted to a third term as senator in a state Trump almost won. Next morning she was on every short list of potential presidential candidates. Supporters say her success with rural voters makes her a formidable candidate in the Rust Belt, while her calm demeanour provides a clear contrast with Trump. Bernie Sanders, Vermont senator Sanders turned a long-shot, anti-establishment bid for the presidency into a “political revolution” that energized the party’s progressive base. His political career began nearly 40 years ago, but it wasn’t until his 2016 run that Sanders became a national figure as a new generation of Democrats – and 2020 contenders – embraced his populist economic policies. Elizabeth Warren, Massachusetts senator Her sharp criticism of Wall Street and big corporations has made Warren a favorite among progressive activists, and she will campaign on a message of a rigged economic system and income inequality.

Black voters are expected to make up 20% of the Democratic party electorate nationally. Party officials have stressed the importance of their vote in next year’s election after black turnout dipped in 2016 when Clinton was the nominee, a crucial factor in her defeat by Trump in Michigan, Pennsylvania and Wisconsin. Restoring the black vote to Obama-era levels could be enough to turn those states Democratic again.

But a question haunting the the party this time is whether, after producing the first African American president in 2008 and a uniquely diverse line-up this time – including six women, six people of colour and an openly gay man – it is going to go back to the future by nominating a straight white septuagenarian male.

‘A little out of touch’

Biden, notoriously gaffe prone, got into trouble last week when he boasted about working with avowed segregationists in the Senate in the name of civility and getting things done. He said of southern Democrat James Eastland: “He never called me boy, he always called me son.” The comment was widely condemned as tone deaf but did not seem have dented his popularity among African Americans when Democrats gathered in South Carolina, which hosts the first-in-the-south primary.

However, Coby Owens, a civil rights activist from Biden’s home state of Delaware, expressed disappointment in the remarks. “I think he’s just a little out of touch with what’s going on with race relations right now,” he said. “What a young African American male has to go through right now in American is not what we should be dealing with in 2019.

“A lot of mothers have to have conversations with their sons or daughters about what to do if you’re stopped by police. A lot of people want someone to stand up and say they understand what that experience is.”

Some candidates will be under particular scrutiny at the debates. Pete Buttigieg, 37, is dealing with the aftermath of the fatal police shooting of a black man in South Bend, Indiana, where he serves as mayor; his poll ratings among African Americans have been dismal. After his pummelling in 2016, Sanders has been working to engage African American voters this time around.

But many African Americans will be watching the this week’s debates to see if the candidates follow through. LaTosha Brown, co-founder of the Black Voters Matter Fund, said: “As black voters, it’s one thing when candidates come to a black church or South Carolina or entertainments specifically tailored for black people, but on these large stages are they going to be able to speak to these issues in our communities? In the past, we’ve seen candidates switch.”

Black voters are very concerned about criminal justice, Brown added, so she hopes the candidates will address the topic in depth. Asked why Booker and Harris are not polling higher among African Americans, she replied: “Racism is so pervasive in this country, there’s no area it doesn’t impact, including the media. I’m not surprised the black candidates are not polling higher than the others.

“A lot of the headlines for weeks were Biden, Bernie, even Buttigieg. How did Beto get up there?! There’s white male bias in the coverage that plays out in the idea of who’s electable and who’s not electable. There is structural racism and the media has been obsessed with white male leadership. We’ve had 45 presidents and only one of them was not a white male.”

No one – black or white – can take black voters for granted, Brown continued. “I think we’re one of the most sophisticated constituencies. We will vote for white folks much quicker than white folks will vote for us. We’ve done it hundreds of thousands of time. Yes, black folks are looking for a black candidate who will reflect their needs and issues, but we have the receipts to show that is not the sole determinant of our vote.

“We are less attached to white male leadership than our white counterparts are. We are open to candidates who are women and people of colour. We are looking for candidates who reflect our values and sometimes they will be black. I don’t think it’s determinant; I think it’s a factor. What’s more of a determinant is we want to win and we know how important this election is.”

In the past African American voters have tended to come together around one candidate, but now their interests are arguably more varied than ever and it is all to play for. Some candidates, such as Senator Elizabeth Warren, appear to be gaining traction, particularly among young African Americans, with proposals including cancelling student debt and strengthening voting rights.

Maurice BP-Weeks, co-executive director of Action Center on Race and the Economy, said: “Joe Biden’s campaign is based on proximity to Obama – perhaps the most popular politician in history and of course wildly popular among black voters.

“I think one of the reasons he’ll fall is one of the same reasons Harris and Booker have not performed as well yet – people want real substantive and structural change. Biden, Booker and Harris fall short of offering that - especially on issues of the economy which are so important to black people. The question is what the underlying value all candidates - regardless of how they identify - are bringing to the table for voters.”