Rubin, who is a conservative columnist, just wrote the perfect column on this subject.  Those are all of the right questions.  
The three most important ones to me are:
1.  Did the Trump campaign have any correspondence with the Russians?
2.  What secrets are in Trump's tax returns?
3.  Which senators, besides McConnell, were blocking the investigation?  Name names.  

Since Trump's taxes are being audited, I would think that the IRS could be subponaed to hand them over.
Until these urgent questions are answered, no inauguration should take place.  This is a Constitutional crisis.