I'm surprised anyone is remotely optimistic about this. Are the Dems saying anything that isn't already known? I'm sure the Senate already knows the facts and has made their mind up on it anyways.
Also if the Republicans all voted against the three evidence amendments, why would any suddenly defect for witnesses unless they're hoping to get a Trump supporter witness? I honestly don't see anything really coming out of except the Reps continuing to support Trump despite the obvious impeachable offense.
Not sure if optimistic is how I would describe myself, but I think the arguments in favor of evidence/witnesses is good enough that we will get there with the 4 GOP senators we need. Could be wrong though, but those senators are severely damaged politically if they get on the wrong side of history here on that issue. In the event that evidence/witnesses are called and allowed all hell is gonna break loose and it'd honestly be tough imho to assume anything about outcomes. I also wanna note that even Trump supporters overwhelmingly support a fair trial and are expecting to see witnesses up there disproving the various charges under oath. I don't wanna give them credit without earning it, but I bet there are many of them who would watch Pompeo and Mulvaney throw Trump under the bus and be utterly devastated themselves. Maybe change minds even. This has happened to farmers and various Trump voters on other matters, mind you. Just need to pop their bubble.
Loads of GOP senators want Trump gone and much prefer Pence in his place. The trick is forcing their constituents to force them to convict, but that requires minds to change. That won't happen imo unless Trump's inner circle is forced to turn against him, which absolutely CAN happen if witnesses are forced to testify. The GOP won't just ignore Bolton either if he is up there slinging shit. That will have at least some notable effect on them I think. So will Pompeo and Mulvaney...these are their old colleagues, remember.
If the GOP just votes to kill all hopes of evidence/witnesses I honestly worry/expect all hell will break loose in the country. The stakes can't be any higher here. Trump will be emboldened even moreso and straight up rig his own election and the GOP will help him do it (more than usual, I mean). I dunno how the public would react to that becoming apparent. Legit scary times.