Simi Valley, California - Republican presidential candidates prepared Wednesday for the second 2024 primary debate, with runaway frontrunner Donald Trump once again reducing the event to a sideshow after refusing to take part.

The 77-year-old former president had announced he would be skipping the debates, citing a commanding poll lead which he has maintained despite facing multiple criminal charges.

Adding to his litany of legal troubles, a New York judge ruled Tuesday that he and his sons Eric and Don Jr committed fraud by inflating the value of the real estate and financial assets of the Trump Organization for years.

The twice-impeached Trump also faces federal criminal charges for the mishandling of classified documents and conspiracy charges for trying to overturn the 2020 election results.

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Instead of the debate, Trump is planning to address former and current autoworker union members in Michigan, a day after Joe Biden's own historic appearance, which made him the first sitting US president to stand on a picket line.

"You know, they're wasting a lot of time with these ridiculous debates that nobody's watching," Trump told supporters at a campaign event in South Carolina on Monday. "Their last debate was the lowest-rated debate in history."

Seven candidates achieved the Republican National Committee's qualifying criteria to appear on stage at the Ronald Reagan Presidential Foundation and Institute in Simi Valley, California.

Trump's chief rival, Florida Governor Ron DeSantis, will face off Wednesday evening against political newcomer Vivek Ramaswamy, former UN ambassador Nikki Haley, Trump's vice president Mike Pence, and former New Jersey governor Chris Christie.

South Carolina Senator Tim Scott and North Dakota Governor Doug Burgum round out the participants who will be present for the clash, televised by Fox Business and Univision.