Mr. Trump may well be correct to assume he has more to lose than gain from these matchups. But it bears remembering that debates aren’t supposed to be primarily for the benefit of the candidates strutting and fretting upon the stage. They are meant to provide voters with a meaty opportunity to judge their options side-by-side, to listen to them field tough questions, to compare their policies and priorities and visions of leadership. The point is to help the electorate make an informed choice.

This is the case for every presidential hopeful. It is all the truer for Mr. Trump, who is dominating the Republican herd. Sure, he’s done the job before. But his performance was … well, unsettling enough that he lost re-election — and then handled the loss rather poorly. Some Republican voters, especially all those suburban women he needs to win back, might care to hear why he thinks they should give him another chance, especially now that he is up to his comb-over in legal trouble. His high-handed decision to skip this debate risks underscoring to these voters how unserious he is about winning their support and expanding his base even a whit, versus staying comfortably focused on his MAGA fans.

Mr. Trump’s participation would reveal much about the other candidates as well. How would the field handle it when he started spewing his conspiracy nonsense? Who would call him out? (If these debate strategy memos are any indication, not Pudding Fingers DeSantis.) Would anyone be able to wrest the spotlight from him?

Even with Mr. Trump missing, there will be much awkward talk of him. (Or so Fox News’s debate moderators promise.) You would think that, if he were in fighting form, he would want to be on hand to keep the pretenders to his throne in line — or, more precisely, to humiliate his critics face-to-face. I mean, lobbing fat jokes at Chris Christie from afar can provide Mr. Trump only so much satisfaction, particularly since Mr. Christie has been calling him a liar, a coward, and a con artist of late.

Instead, the former president is taking the cheap and entitled way out, fulfilling at least one of Mr. Christie’s critiques. After weeks of being tiresomely coy about his debate-night plans, he has decided to sit down with the disgraced pundit Tucker Carlson, The Times reported on Friday. The man is notoriously fickle, so who knows when — or even if — this will actually happen. Let’s hope it doesn’t. I’m sorry, but we already watched Mr. Carlson give Mr. Trump a thorough bootlicking back in April, not long before Fox News gave Mr. Carlson the boot, in fact, and it was sad. Worse than watching Don Jr.’s videos-for-hire on Cameo. No one needs to see more of that.