That explains how he got almost half the votes on election night, but it does not explain the 1/3 that still to this day support him 100%. There is a pretty substantial underlying problem in play and Trump is the symptom, but the problem is deeper than a malfunctioning political system.
It is almost unheard of in the US for an elected politician to poll lower than 30%, it seems to be a floor. This is for both parties, and all sorts of terrible behavior.
That explains how he got the votes on election night in 2016. A vote for Grump in 2016 was completely understandable. But he should have plainly been a one term president, after his abjectly terrible handling of Covid (for starters, we needed leadership rather than dividership). But unfortunately in our upside-down world, Covid actually handed Grump a big excuse for why his first term was such an exercise in failure. And if there is one thing Grump is good at, it's weaseling responsibility onto others - a quality that his followers greatly admire as it soothes their own consciences as well.