Rosenstein is a Mueller/Comey guy. He helped bury Uranium One, which helped Hillary and Obama. His wife is a big DC lawyer who works for a law firm that does lots of work for the Clintons and Obama. I believe she has personally done some of that work herself.
Another poster clued me in. I really did not know since I kept hearing Trump appointed him, but i now understand how that worked. He is dirty and it makes sense now.