I think the Clinton Foundation stuff terrifies the mainstream media because if fully exposed, there would be a lot of Democrats other than just the Clintons who will have a lot of 'splaining to do. I''m about as far from Conspiracy Guy as it gets, but that thing just stinks.
Trump sort of has an out anyway. He can say "I donated to it before I knew about all this other crap, thinking it was a legitimate charity. But now, I want to know where my money went!"
And that'd probably work.