When Ulysses Grant left office, he went back to being Mr. Grant. Sure, he'd been a general (he'd been the general, but he wasn't serving any longer) and he'd been president (but the whole point to being President, rather than a king, is that you stop doing it). So, by address, Mr. Grant.
At least since President Carter, that hasn't been true; it's still, by address, President Carter, President Clinton, President Bush, President Obama.
That's a mistake; that's making the presidency holy, instead of a job. Once you do that, you can't think about it accurately; it picks up this nonsensical air of immutability rather than being a job, and the current holder of the job being subject to material evaluation.
Holiness has been undone before; the House of Hohenzollern is still rich, still owns (and sometimes inhabits) castles, but the head of the house is Mr. Hohenzollern. And that was with a fair number of people who did not want it undone, rather as there are a fair number today who demand a king and will not have the president be anything other than holy.
One of the best simple things a hypothetical Biden admin could do would be to change the protocol rules, and get real strict about former presidents losing the title of address. Yeah, sure, you had the fate of the world in your hands for awhile, but you put it down. The brimstone whiff of the mushroom cloud and soulless glint of the market attend on you no longer.
And, yeah, sure, Trump hasn't got his own fate in his hands. Trump's haplessness is not the point; the point is that which is public is not, after all, that which is holy. If you try to make the simple material necessity of the public sphere -- the requirement to keep the minimum qualification for civilisation and maintain for all citizens the odds of dying of violence or starvation so low as to be immaterial -- a holy thing, you wind up with something that isn't civilisation or in any respect holy.
You'd think more people would notice.