"This is the trial of a criminal."

This little sentence completely undermines your case. If a UK newspaper printed that about a public figure without a criminal record yet to be brought to court it would compromise the process to such an extent that the accused person would quite rightly be able to claim that a fair trial was now impossible. In addition, as Trump can't be punished (by fine or imprisonment) even if convicted by the Senate, the process can't be regarded as in any way equivalent to due process in federal law. You are making the mistake of equating terms used in federal law with what may happen in the Senate: there will be no vetted or sworn-in jury; you are using terms such as "crime" and "convicted" in a loose, generic sense when, in law, you would rightly be pulled up for so doing (it's fine to say "it would be a crime to overcook this beautiful piece of fish" because we'd all know what you meant, whereas in Trump's case you are tendentiously prejudging the issue before he's been tried). As for witnesses, the Senate doesn't even have to call any (they didn't last time), and likely won't do so, as the last thing the Democratic Party wants is for Biden to have to endure the distraction of a protracted process. If you did that in federal law you would be accused of setting up a kangaroo court; as Trump can't be punished by a Senate trial, the process can't be regarded as being in any way equivalent. Even the term "trial" here is not equivalent to what happens in due legal process, much as you would like it to be. He can be tried in the ordinary courts later. One step at a time. It's all in your constitution.

One more point about witnesses and victims. Trump's alleged crime is not that he stormed the Senate. He is accused of whipping up a mob in a speech. How many Senators were in that crowd? I'm afraid that "I saw it on the telly" doesn't cut it. Camera angles, editing, etc... Senators who were attacked physically, or intimidated by a mob, are victims of a different crime yet to to be called up. You can perhaps see how this might go if loose interpretations and loose terminology are used. He will have a legal team who'll jump all over you.