That's just not true. The presumption of innocence merely frames the roles of court participants - the prosecution must produce sufficient evidence to prove the defendant is fully beyond reasonable doubt.
Vigilantes are going to judge the accused regardless.
Additionally, if a legal system I'd unable or unwilling to try a case then IMO the public can form their own conclusions. Perhaps one day Trump will face judgement, but it's undeniable that he's received special treatment during these proceedings.