Charleston, South Carolina - President Joe Biden reached out to Black voters Monday in an emotional campaign speech at the site of a racist massacre in 2015, but hecklers calling for a Gaza ceasefire highlighted another problem area for the Democrat.

Biden said the "poison" of white supremacy had "no place in America" in his address at the Mother Emanuel AME Church in Charleston, South Carolina, where nine Black parishioners were murdered by a racially-motivated killer.

The 81-year-old then linked efforts by Republican former president Donald Trump to overturn the last election in 2020 to the wider US history of racism, calling it the "old ghost in new garments."

"They're trying to erase history and your future, banning books, denying your right to vote and have it counted," Biden told the congregation from the pulpit of the historic church.

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Biden later met with survivors of the shooting, the White House said, continuing a long connection with the church which started when he visited as vice president under Barack Obama after the killings.

Self-proclaimed white supremacist Dylann Roof, who was 21 at the time, said he carried out the shooting to start a race war. He was sentenced to death in 2017.

The speech was the second of two events kicking off Biden's 2024 campaign in which he has targeted Trump, whom he is expected to face in a closely-contested rematch in November.

Minutes into Biden's speech, however, he was interrupted by a demonstrator who said that if the president cared about lives lost then he should call for an end to Israel's assault on Gaza.

A small group of protestors then began shouting "ceasefire now" before they were drowned out by churchgoers chanting "four more years" in support of Biden's bid for a second term. Biden said of the protesters that he could "understand their passion," before adding, "I've been quietly working with the Israeli government to get them to reduce and significantly get out of Gaza."

Both the speech and the interruption reflected the diverse electoral groups that Biden must reach out to in what promises to be a difficult battle for reelection.

Polls show Biden's support slipping among Black, youth, and ethnic minority voters, who helped drive his 2020 election win against Trump.

Biden also faces opposition from many Democrats over his staunch support of Israel's brutal campaign against Gaza following the October 7 attacks by the Palestinian militant group.

The current president will need support from multiple constituencies as he is either trailing or neck-and-neck with Trump in a series of recent polls, while his approval ratings are the lowest for any modern president at this stage in their term.

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Biden's fired-up speech Monday touched on emotional topics as he sought to connect to voters, ranging from his stated support for civil rights to his Catholic faith and the church's support after his eldest son Beau died of brain cancer at the age of 46 in the month before the massacre.

The choice of South Carolina was also symbolic because it was his victory there in the 2020 Democratic presidential primary that helped revive his flagging candidacy.

Biden's campaign said his remarks in Charleston underscored the "enormous stakes of this election."

"We're all proud to welcome President Biden to the church to remind the nation of what happened and that it is on all of us to fight back against this extremism," Biden campaign co-chair and congressman Jim Clyburn said.

He said the church had "witnessed the horrors of hate-fueled political violence" and "shown us the path forward after moments of division and despair."

Biden has set his sights squarely on Trump as the election year begins, portraying himself as a unifier and defender of democracy, and his opponent as a threat to American institutions.

He has also changed his focus from talking about the economy, with many voters still unconvinced by favorable jobs and growth numbers while prices for food and housing remain eye-wateringly high.

But signs of further Democrat concerns emerged over the weekend, with reports that ex-president Barack Obama had raised questions with Biden about the structure of the campaign.