If Senator McConnell and his Republican colleagues truly believe that the Democratic case for impeachment is so weak, a sham, wouldn’t it be to their political advantage to run a proper trial, to give the appearance of impartiality, and then acquit Trump. They have certainly prejudged the case, so that is a foregone conclusion. Why not subpoena Mulvaney and Bolton and have them support the President’s version of things under oath? And apparently Trump wants a real trial, not some quickie; he wants to be vindicated.
There is only one reason: they fear that more of the public will come to support impeachment after being exposed to the facts in such a trial, perhaps even some Republican Senators. And what if Mulvaney and Bolton support the Democrats’ charges, not Trump’s version of things? That would really throw a wrench in things.
There is no way that McConnell will change his posture, unless Trump forces him to. Democrats only hope is that when they challenge the process in various ways with Chief Justice Roberts, who will be the Presiding Officer and under the rules of the Senate controls all aspects of the process … although he can be overruled by a simple majority … he will side with them.
In that case, if the Republicans overrule his decisions, that would expose the whole Republican stance as dishonest and a farce to all but Trump’s devoted base. The Democrats will have won even if Trump is acquitted.