Assume, for purposes of argument, that McConnell and the GOP majority in the Senate go with my Option #1, and refuse to call any witnesses; the decision would, therefore, be made solely on the basis of the record provided by the House. What does that mean for the rationale for acquittal?
It means the credibility of the witnesses in the House proceedings cannot be effectively attacked, and the GOP senators can’t use the favorite talking point of their House counterparts–that the process was fundamentally unfair to Trump–as the basis for their vote. That leaves them with two possible rationales. The first–that there is insufficient testimony from anyone with first hand knowledge of Trump’s statements and motives to support removal–will look absurd to anyone reading about the case 20 years from now, given that the Senate was presented with the opportunity to call several such witnesses and declined. The second is that Trump’s actions, while reprehensible, are not enough to merit impeachment. This line of reasoning will both enrage the president and send a message that coercing a foreign nation to intervene in American elections is not a big deal. That isn’t a message that is going to make Collins or Murkowski feel very comfortable.