From the appointment of Mueller, Rosenstein’s more serious conflict has undermined the investigation. Rosenstein is not just a witness to Mueller’s obstruction investigation, he is one of the key witnesses. Trump consulted Rosenstein before firing Comey, and Rosenstein wrote a memorandum effectively calling for his removal. Initially, the White House suggested that Comey was fired due to that memorandum, and Rosenstein reportedly was irate. The White House then had to walk back the statements after Rosenstein demanded a correction. That puts him at ground zero of the obstruction allegations.
Despite the fact that he is a key witness in Mueller’s investigation, Rosenstein has continued as Mueller’s boss, approving any expansions of his mandate and other issues. The investigation could have a pronounced impact on Rosenstein’s professional standing. Rosenstein has portrayed himself as above the fray, a bulwark against Trump’s reported desire to lay waste to the investigation. He is Mueller’s primary line of defense. Yet, Mueller has to question Rosenstein’s own conduct and subsequent accounts if he is to do a complete investigation of Comey’s firing. Rosenstein also is a key player in some of the secret FISA warrants targeting Trump’s campaign aides in the Russian investigation.