So you would like total transparency of all conversation that Hillary, Sanders or Trump may have with their wealthy donors?  

It would certainly be interesting.  
It would likely be a denial of our rights to privacy.   
I'd like to hear those conversations myself!    

Written documents might help, but there is a reason for the old saw, 'most business takes place on the golf course'.   It is not difficult to hide conversation.   In the private sector it's a given.     

There is trust among thieves, small time or billionaires, that requires an oath of secrecy.   Break that unwritten code and you will be treated with extreme prejudice.  It's only a 'moral' decision if you accept the responsibility and the risk of consequences.     

*Lot's of anonymous people make claims of piety or ethics when they know they can't be held accountable.