Donald Trump’s chief rivals for the Republican nomination have attacked him for his absence at their party’s second 2024 presidential debate.

Florida Governor Ron DeSantis, polling a distant second in the race, slammed Mr Trump for being “missing in action”.

More than 2,000 miles (3,200km) away in Detroit, Michigan, the former president sought to woo striking auto workers.

The eventual Republican nominee will face President Joe Biden, the likely Democratic candidate, next year.

On stage for the Fox Business Network’s primetime showdown are Mr DeSantis, biotech entrepreneur Vivek Ramaswamy, former UN Ambassador Nikki Haley, former New Jersey Governor Chris Christie, former Vice-President Mike Pence, South Carolina Senator Tim Scott and North Dakota Governor Doug Burgum.

Former Arkansas Governor Asa Hutchinson, who appeared at the first debate last month in Milwaukee, Wisconsin, did not qualify to participate Wednesday night at the Ronald Reagan Presidential Library in Simi Valley, California.

Polite exchanges marked the first half hour of the debate, before several candidates piled on against Mr Ramaswamy, who has seen a polling bounce since the first debate.

The former entrepreneur, who has focused his foreign policy interventions on the threat posed by an ascendant China, faced criticism over his past business dealings in the country.

Mr Pence offered Mr Ramaswamy back-handed praise for pulling out of a Chinese deal in 2018, saying it “must have been about the time he started voting in presidential elections”.

But Mr Ramaswamy, a brash political novice with highly unorthodox policy proposals, smiled about being “interrupted by a lot of people here”.

In other forceful moments, he claimed that being transgender was “a mental health disorder” and that children under the age of 16 should be barred from using social media.

“Every time I hear you, I think I get a little bit dumber,” a visibly infuriated Ms Haley hit back. “We can’t trust you.”

Another ex-businessman on the stage, the low-polling Mr Burgum, interrupted the forum on several occasions to argue it was time to “treat the taxpayer like a customer”.

But some like Mr DeSantis, who has struggled to eat away at Mr Trump’s lead without angering his loyal supporters, also zeroed in on the elephant not in the room.

Mr Christie, long an arch critic of the former president, argued that Mr Trump was too afraid to defend his record in office, adding: “We should call you Donald Duck.”

Mr Trump, who leads his Republican challengers by about 40 points in most opinion polls, had long indicated he would skip the event.

He has said his dominance over the rest of the field would only be undermined by showing up, also alleging bias in the choice of debate moderators and venue.

In a speech at an auto supplier in the Detroit suburbs, Mr Trump barely mentioned his opponents, except to say they were “all competing for a job” in his administration if he wins.

His remarks came one day after Mr Biden, in a first for a sitting president, joined a picket line with auto industry workers at the labour union’s invitation.

Mr Trump, who spoke at a non-unionised factory, slammed the president’s push for electric vehicle production and warned workers they were “all going to be out of business”.

And he repeatedly called on UAW leaders to endorse his presidential bid, telling workers to “get your union leaders to endorse me, and I’ll take care of the rest”.

It was an early skirmish in the battle for the blue-collar vote, and their most direct face-off so far, ahead of next year’s election.

A CBS News poll conducted earlier this month found Mr Trump beating Mr Biden by one point in a rematch of their 2020 head-to-head.

Republican voters will begin choosing their candidate in state-by-state contests in January, with the first taking place in Iowa.

The winner will be formally crowned at the party convention in Milwaukee in July and go on to the general election less than four months later.