This leak sounds like it was done to attempt to provoke Pres. Trump into firing Mueller and/or (more likely) it is an attempt to deflect from the story of the anti-Trump texting Peter Strzok.
That would be a big mistake. Since Trump is (i believe) innocent of any wrongdoing in the Russia case, he want’s the most rabid Trump hating investigators possible. They will go overboard and expose themselves like they have been doing for the past several months. I smell a little Steve Bannon straterery here.
Maybe Muller set up a leaker.