Like with most investigations such as this, what will probably come out, is that Trump didn't do anything, but his people did.  Where they are going to nail Trump, is on obstruction, just like with both Nixon and Clinton, it wasn't the original crime that got them, it was the cover up.  Even if he did nothing, if he tries to kill the investigation, that basically is obstruction.  Someone should mention that to Trump.  

Ultimately, if the Rs didn't think these investigations had merit, they wouldn't have hearings.  They have to think that there is more to the story than we currently know.  Constantly blaming the Ds for this just makes it look like you don't really understand how things work.