from the article: "But why Rosenstein's briefing needed to happen in a room designed for classified briefings is still unclear. McConnell aides wouldn't say whether Rosenstein requested that the briefing be classified or whether he has told Senate leaders that he has classified information to share."

Rosenstein should resign if he wrote the letter, essentially for Trump, knowing that Trump planned to fire Comey.  He works for the JUSTICE DEPT - he's not a White House Council!  I hope this puts an end to his role in our Federal Government.  Typical CYA Washington politics by all.