The latest move by the Senate might be an indicator of  a number of Senators who  are very concerned on how these investigations will end.  It was  far better politically to  be on the side that got Nixon than those who would not admit what happened.  Now those who stand with Trump are betting their support will not bite them should the finding show more than a casual relationship between Putin,Trump and his campaign staff existed. It is a win win for Senators who are pursuing an investigation.  Those in support of the investigation can point to the results of the investigation as being an indicator of their commitments no matter the findings.  Those opposed risk being on the wrong side of the results.