And Mueller is working with state law enforcement. These are less restricted on who they can/can't indict, but more importantly in context, could shut down his businesses and sue for crippling amounts if proof of lawbreaking is found.
While it's well-known that Mueller is working with the New York AG's office, what I'd be more interested in seeing is Mueller working with Delaware. DE is a well-known corporate tax haven, and even Trump has at least one "company" there that is loaning millions of dollars to Trump's other companies at prime plus five percent. We saw this earlier when looking at his fiscal release forms that he says are as good as tax forms no really why are you laughing they are. We've seen this company doing other things as well. If Trump and his companies are involved with money laundering -- especially overseas money involved with his campaign -- it could Jenga a substantial part of his company propped up by loans to himself.