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.
Instead of the debate, Trump is planning to address former and current autoworker union members in Michigan, the historic heart of the US car industry and a key battleground for the election campaign.
His visit comes a day after Joe Biden's appearance in the Midwestern state, where he became the first sitting US president to stand on a picket line, as both men bid to sell themselves as the candidate for the American worker.
"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."
Gerard Filitti, senior counsel at the Lawfare Project, says Trump's standoffish strategy is intended to send the message that he is the "inevitable" choice to be the Republican standard-bearer in 2024.
"He has nothing to gain by debating, and everything to lose if confronted with questions about his past conduct, the multiple criminal indictments he is facing regarding the 2020 election, and even his lack of clarity or consistency on some issues like abortion," Filitti told AFP.
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 the mercurial tycoon's chief antagonist, 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.
- Unwarranted arrogance? -
Just under 60 percent of Republican primary voters in a new NBC News poll say Trump is their top choice in the crowded primary, with DeSantis trailing at 16 percent. None of the other candidates achieves double figures.
Trump's legal troubles have done little to dent his lead. He has remained the Republican's likely choice for a presidential candidate despite Tuesday's ruling that could see him ousted from management of the Trump Organization.
The former president denounced the ruling -- along with previous charges over alleged hush-money payemnts and sexual abuses -- as a "witch hunt".
Filitti cautioned that while Trump's absences from the debates do little to harm him in the primary, they could hurt his standing among traditional Republicans in the general election.
"In fact, his refusal may well be perceived as unwarranted arrogance by many Republicans that are not among his base of supporters, as well as by independents," he said.
For DeSantis, the showcase presents a second chance to close the polling gap and woo donors, although his well-received performance in the first outing in Milwaukee last month did nothing to dent Trump's lead.
Recent polling has indicated that Haley, a former South Carolina governor as well as a Trump administration figure, would likely fare best of all the candidates in a head-to-head vote against President Biden, and she will be keen to frame herself as the only candidate capable of wresting the White House from the Democrats.
The prevailing view on the other side of the aisle is that, regardless of the candidates' debate performances, the Republican primary is a done deal.
"It's all for theater and/or the hopes of making a good enough impression to land a job with the Trump White House or to fuel other political aspirations," Democratic election strategist Amani Wells-Onyioha told AFP.
"But these folks know none of them will become president at this time."
