At least six Republican candidates will take part in the second 2024 Republican presidential debate on Wednesday in California. Donald Trump plans to skip the event and give a speech in Detroit to autoworkers.

Here are the candidates expected to be on stage for the debate, which begins at 9 p.m. ET (0100 GMT on Sept. 28) at the Ronald Reagan Presidential Foundation & Institute in Simi Valley, California:

RON DESANTIS

After a glitch-filled campaign launch in May on Twitter, now called X, DeSantis has positioned himself to the right of Trump on a number of key social issues such as abortion. But his well-funded campaign has struggled to gain traction, and his top donor has said he won't give the Florida governor more money unless DeSantis adopts a more moderate approach.

DeSantis, 45, is Trump's top rival, but remains nearly 40 percentage points behind the former president in opinion polls. He has fired staff and rebooted his campaign several times since May, but those steps have done little to boost his candidacy. DeSantis' campaign says it is focused on stopping Trump in Iowa, where the party will hold its first nominating contest in January.

MIKE PENCE

Trump's vice president has broken with his former boss over Trump supporters' Jan. 6, 2021, attack on the U.S. Capitol as Pence was inside, presiding over Congress's certification of Democrat Joe Biden's 2020 victory. Pence, 64, says, "history will hold Trump accountable" for his role in the attack.

A staunch conservative, the former Indiana governor is appealing directly to the evangelical Christian community, but his campaign has struggled to raise money, and he is stuck in the low single digits in polls.

VIVEK RAMASWAMY

A former biotechnology investor and executive, Ramaswamy, 38, has pressured firms to abandon environmental, social and corporate governance initiatives. The political outsider has stoked grassroots chatter as a potential alternative to Trump, and had a strong performance at the first debate in Milwaukee in August. Ramaswamy is a fervent supporter of the former president, and says that if he won the White House, he would pardon Trump.

NIKKI HALEY

A former South Carolina governor and Trump's ambassador to the United Nations, Haley, 51, has emphasized her relative youth compared to President Biden, 80, and Trump, 77, as well as her background as the daughter of Indian immigrants.

Haley has gained a reputation in the Republican Party as a solid conservative who has the ability to address issues of gender and race in a more credible fashion than many of her peers. She has also pitched herself as a stalwart defender of American interests abroad. She has single-digit support among Republicans, according to opinion polls, although she saw a slight uptick in support after a strong first debate performance in August.

TIM SCOTT

The only Black Republican U.S. senator has low name recognition outside his home state of South Carolina, but his optimism and focus on unifying his divided party have helped him draw a contrast with a more aggressive approach from Trump and DeSantis. Scott's supporters, however, acknowledge that while his sunny demeanor is a selling point, it may not be enough to win. Scott, 58, attracted 2% support among Republicans, according to a Reuters/Ipsos poll conducted from Sept. 8-14.

CHRIS CHRISTIE

Christie, 61, advised Trump's White House campaign, but became a vocal critic of the former president after the Jan. 6, 2021, attack. The former New Jersey governor and federal prosecutor stepped up his verbal attacks as Trump faced a growing number of criminal charges.

Christie received 2% support among Republicans in the latest Reuters/Ipsos poll.

(Reporting by Tim Reid, editing by Ross Colvin)