Right, which is most akin to the indictment process in a criminal trial.
Criminal trials introduce new witnesses and evidence all the time that never went to the grand jury.
According to the roles of the impeachment process assigned to the House and Senate, the Senate cannot develop evidence, it can only judge an article of impeachment as delivered by the House
The Senate has the sole right to try the case.
What part of that formulation limits the trial to be something much less than all other trials in our system?
They are not trying a "case". They are judging the merits of whatever case is put forth by the House in whatever article of impeachment is being presented to them. The Senate, as judge, cannot be part of the prosecution effort, of which developing or introducing "new" evidence or testimony would fall. This is a House responsibility alone that the constitution expressly prohibits the Senate from being a part of. They, the Senate, can ONLY consider whatever current evidence that comprises the current article of impeachment before them. Bolton's "new" testimony is not part of the current article of impeachment evidence or testimony. It is off limits to the Senate until such a time that the House presents an article of impeachment that contains it. No one is keeping the House from doing this. They are asking the Senate to do the job assigned specifically to the House by the Constitution. The Senate should refuse.
However it's supposed to work in theory, the House delivered a sentence to the Senate, not a case. Not one exculpatory witness was permitted nor were clearly pertinent documents allowed to be entered into evidence.
With what they were delivered, the Senate is actually a group of lawyers looking at either the defense presenting the case for dismissal, retrial, or a plea bargain that falls short of the theoretical single sentence the Senate can deliver which is removal from office.
Looking at what is going on in the Senate and comparing it to any other trial not tossed out as a mistrial as soon a mistrial is requested is a bit silly. The House threw out first presumption of innocence, then the right to confront your accuser, and finished up with denying the defense the right to call witnesses or exculpatory documents.
Given the specific circumstances of this circus, what you're arguing is that the Senate should be held to the very same standards that would have prevented the House from ever delivering the articles of impeachment in the first place if the House had stuck to those standards.
JMHo