Mueller was about Russian interference and conspiracy to help them interfere in the US Election. From the wikipedia page on this...some interesting commentary
George Croner of the Foreign Policy Research Institute has also expressed his concerns with what he describes as a "curiously flaccid" approach taken by Mueller in dealing with what the public would normally interpret as "coordination". He sees Mueller's dependence on a formal "tacit agreement" approach as "an overly cautious" and "legalistic construct":
I think "Rusher, if your listening..." was bad enough.