From a Los Angeles Times editorial:
Debate moderators can’t hold candidates in contempt of court, levy fines or have misbehaving candidates physically removed, but they aren’t without the authority to keep participants on track. For instance, they can deal decisively with nominees who bluster, bully, ignore time limits and engage in name-calling by shutting off their microphones.
…
In an open letter calling for Trump and Biden to debate, a group of news organizations (not including the Los Angeles Times) wrote: “If there is one thing Americans can agree on during this polarized time, it is that the stakes of this election are exceptionally high. Amidst that backdrop, there is simply no substitute for the candidates debating with each other, and before the American people, their visions for the future of our nation.”
Yet for debates to fulfill that function there must be rules of civility and common decency — and candidates must abide by them.