Once again, Trump confuses venues. Innocent until proven guilty is applied to criminal defendants in a US court.
There are other measures. In a civil court, the standard is something like the preponderance of the evidence. In a job interview, it is what the hirer wishes, so long as they don't breach government guardrails. In diplomacy, it is none of the above.
I take the point that one shouldn't rush to judgement. But here we see a US president operating as wingman for the Saudis who have provided no coherent explanation for the disappearance of a man who entered their embassy, and never exited it. If they can't produce the man from inside, then they likely committed the crime.
In such circumstances, presuming innocence is either naive or motivated by some other purpose. Trump, of course, wants to sell weapons to juice the economy, regardless of where those weapons end up.
Some folks will call that an awesome display of disgusting morals. Not "the greatest country on earth" by any recognisable standards.