Eh, it's more that whatever the structural error is, that error infects the fundamental trial process. (Hence, one need not demonstrate prejudice from the error as one does with non-structural constitutional error, at least if it is preserved).
So for example, if the courtroom is closed without requisite findings being made following the proper procedure, there is structural error that infects the entire trial, even if that error only happened during jury selection alone (aka, not "from the beginning of the proceeding until the end of it.)
I did say "generally and briefly" but for the sake of argument...
Structural errors are structural defects in the constitution of the trial mechanism affecting the framework within which the trial proceeds.
United States v. Soto, 519 F.3d 917 (2008). Such structural errors involve basic constitutional protections, without which a criminal trial cannot reliably serve its function as a vehicle for determination of guilt or innocence. They require reversal without regard to the strength of the evidence or other circumstances. It is only for certain structural errors undermining fairness of criminal proceeding
as a whole that even preserved error requires reversal without regard to mistake's effect on proceeding. Etcetera.
There's also a harmless error analysis that goes hand in hand with a structural defect analysis, but a key part of the structural error analysis is that its presence undermines the whole of the proceeding, which, most simply stated, is that the process is undermined from the outset, which in turn denies a fair trial. For example, jury impossibility where the right of peremptory challenges are denied can bring about a structural error analysis. So can what's known as speculative impossibility (which generally has to do with a biased judge or a defendant being denied right to choice of counsel when he can facilitate such a choice). It's also possible that some jury composition claims would fit in this category--especially Batson claims, where the problem is with the process of selection, not necessarily with the jury ultimately seated, and the injury is at least in part to the excluded jurors rather than to the defendant.
So what you'll see most often is that something has occurred from the outset of a trial that renders the proceeding unreliable. There are also doctrines of "seriousness" and "obviousness" which may come into play when analyzing structural defects, but this post is long and boring enough already.
Suffice it to say that Trump is in no way acquainted with any of the concepts we're discussing.
