Nothing for Trump to gain? He could demonstrate that he’s not senile like Biden. He could defuse his “blowhard” image, ex. “Desanctimonious”. He could attend and be genial and respectful of the other hopefuls. Refusing to show up won’t help him imo.
Whatever President Trump says or does in a debate will be distorted and used to injure him politically. That’s what won’t help.
It’s a good strategy, if you are ahead.
President Trump is vulnerable on issues like spending when Republicans controlled the House and the Senate, and the Second Amendment.
It’s best for him not to debate as he’s not prepared to answer questions related to those areas.